JP5043450B2 - Serial communication system and slave device - Google Patents

Description

  The present invention relates to a system, an apparatus and a method for realizing serial communication, and an application thereof.

  Conventionally, serial communication is used in a system including an image forming apparatus and its optional device. According to Patent Document 1, in a serial communication system including a master device and a slave device, a method is proposed in which the master device notifies the start of communication by changing one level of a clock signal and a data signal. .

Further, according to Patent Document 2, a master device to which a plurality of slave devices are connected adds unique information for recognizing each slave device to data and transmits the data to a plurality of slave devices. A method for monitoring the state of the system has been proposed.
JP 2006-135545 A JP 2006-225108 A

  According to Patent Document 1, there is an advantage that a handshake for transmitting data from the master device can be realized without increasing the number of signal lines. However, in the invention described in Patent Document 1, handshaking when data is transmitted from the slave device to the master device after the data reception from the master device is completed is omitted. For this reason, the slave device always waits for a certain period of time after receiving data from the master device before transmitting data. This waiting time may be too long or too short depending on communication conditions, and there is room for improvement.

  When a plurality of slave devices are connected to one master device, the time from when data is received from the master device to when all slave devices transmit data is also managed as a fixed time. For this reason, it takes a very long time for all slave devices to transmit data to the master device. On the other hand, if data reception from the master device is not completed within a predetermined time, there may be a slave device that cannot transmit data corresponding to the data from the master device.

  According to the invention described in Patent Document 2, the master device does not need to perform communication for state monitoring for each slave device, and there is an advantage that the number of communication can be reduced. However, in the method of Patent Document 2, when it is desired to monitor the status of each slave device, the communication of requesting and acquiring the status information of the slave device is always required once, so the real-time property of the status information is lost. It is easy to end up.

  Accordingly, a first invention described in the present application aims to realize a handshake when transmitting data from a slave device to a master device without providing a dedicated line for handshaking, for example. The second invention described in the present application is intended to facilitate maintaining the real-time state information. Other issues and purposes will be understood from the entire specification.

The present invention can connect a master device and a plurality of slave devices, a clock signal line for transmitting a clock signal from the master device to the plurality of slave devices, and the master device in synchronization with the clock signal A command signal line for transmitting a command signal from the slave device to the plurality of slave devices, and a status indicating its own state from at least one slave device of the plurality of slave devices to the master device in synchronization with the clock signal A status signal line for transmitting a signal, and a signal provided on the slave device, the signal level of the status signal line being switched from the first level to the second level to notify that the preparation for transmitting the status signal is ready A notification means; and a transmission means provided in the master device and transmitted from the notification means provided in the slave device. Is provided with a detecting means for detecting that the signal level of the status signal line becomes the second level, wherein all of the plurality of slave devices, after receiving the command signal from the master device, said command Regardless of whether or not an instruction to return a status signal is received by the signal, when the preparation for transmitting the status signal is completed, the signal level of the status signal line is switched to the second level, and the master device After transmitting the command signal to all of the slave devices, when the detection means detects that the signal level of the status signal line has become the second level for all of the plurality of slave devices, the status signal is transmitted. So that the clock signal is transmitted to all of the plurality of slave devices. Providing serial communication system characterized by Gosuru.

The present invention also provides a clock signal line for receiving a clock signal from a master device, a command signal line for receiving a command signal from the master device in synchronization with the clock signal, and a clock signal. A status signal line that transmits a status signal representing its own state to the master device synchronously, and by switching the signal level of the status signal line from the first level to the second level, Notification means for notifying the master device that the slave device is ready to transmit the status signal, and when the command signal is requested to transmit the status signal to the master device, after the signal level of the status signal line is switched to the second level, before in synchronization with the clock signal If the status signal is transmitted through a status signal line and the command signal does not request transmission of the status signal to the master device, another slave that is requested to transmit the status signal to the master device In order to transmit the status signal from a device to the master device, a signal level of the status signal line is switched to the second level, and a slave device is provided.

  According to the present invention, when the slave device notifies that it is ready to transmit the status signal, it is possible to transmit data from the slave device to the master device without providing a dedicated line for handshaking. Handshake can be realized. Further, according to the present invention, the state information is transmitted from the slave device to the master device in synchronization with the clock signal for receiving the command signal, so that the real-time property of the state information can be easily maintained.

  An image forming apparatus equipped with a serial communication system according to the present invention will be described with reference to the drawings. In the embodiment, an electrophotographic multicolor image forming apparatus is introduced as an example. However, the present invention does not depend on an image forming system or a difference between single color and multicolor. The present invention can also be applied to electronic devices (computers, peripheral devices, information processing devices, home appliances) other than image forming apparatuses. However, the effect of the present invention is particularly easily exhibited in the master device as long as a plurality of slave devices can be connected.

  In addition, data (command signal) received by the slave device from the master device is referred to as “command”, and status information (status signal) transmitted from the slave device to the master device is referred to as “status”.

[Embodiment 1]
In the present embodiment, the master device corresponds to a main body device of a color laser printer, and the slave device corresponds to an optional device (for example, an optional device or an optional paper discharge device that can be added). The main device executes serial communication using a common clock when transmitting / receiving data to / from each option device. In particular, the main device and the optional device can realize the handshake without providing a handshake dedicated signal line when performing communication between the main device and the optional device. For example, when the status is returned in response to the received command, or when the status transmission is completed and the next command is received, the optional device changes the signal every time the reception / transmission operation ends, Realize handshake.

(Main unit)
FIG. 1 is an overall configuration diagram of an image forming apparatus commonly applied to each embodiment. The image forming apparatus 100 includes four image forming stations. Each station has a photosensitive drum 1 as an image carrier. Around each photosensitive drum 1, a charging device 2, an exposure device 3, a developing device 4, a transfer member 5, and a cleaning device 6 are arranged in order according to the rotation direction. The charging device 2 uniformly charges the surface of the photosensitive drum. The exposure device 3 forms an electrostatic latent image on the photosensitive drum by irradiating a laser beam based on the image information. The developing device 4 visualizes a toner image by attaching toner to the electrostatic latent image. The transfer member 5 transfers the toner image on the photosensitive drum to a sheet. The cleaning device 6 removes post-transfer toner remaining on the surface of the photosensitive drum after transfer. Here, the photosensitive drum 1, the charging device 2, the developing device 4, and the cleaning device 6 are integrally formed into a cartridge to form a so-called process cartridge 7.

  The feeding unit includes an option device 20a and option devices 20b and 20c. The sheet fed from the feeding unit is transported to each station by a transport device 9 constituted by a transport belt, and each color toner image is sequentially transferred to form a multicolor image. The fixing device 10 heat-fixes an unfixed image on a sheet. Finally, the sheet is discharged to the discharge device 50. The discharge device 50 is, for example, a sorter.

(Feeding department)
The option device 20a is a feeding device built in the main body device, and may be called a main body feeding portion. The pickup roller 21a separates and feeds the sheets one by one. The transport rollers 22a and 23a transport the paper further downstream in the transport direction. The sheet fed from the feeding unit is transported to the transport device 9 by the registration roller 15. Note that since the optional device 20a is built in the main device, it may not be generally called an optional device. However, in the present specification, since the option device 20a also operates as a slave device of the serial communication system, it is treated as a type of option device.

  The option devices 20b and 20c are optional feeding units that can be connected to the main device. The option device 20b separates and feeds the sheets one by one by the pickup roller 21b. Thereafter, the sheet is conveyed to the option device 20a via the conveyance rollers 22b and 23b of the option device. The option device 20c separates and feeds the sheets one by one by the pickup roller 21c. Thereafter, the sheet is conveyed to the option device 20b located in the upper stage via the conveyance roller 22c and the conveyance roller 23c of the option device. Note that the paper may be called, for example, a recording material, a recording medium, a sheet, a transfer material, or a transfer paper.

  Reference numerals 24a, 24b and 24c denote sheet sensors for detecting paper. Information indicating the presence or absence of paper detected by the sheet sensors 24a, 24b, and 24c is a good example of status information. Generally, the image forming apparatus executes various controls (conveyance control and image formation control) starting from the timing when the leading edge of the paper arrives. In particular, in order to increase the throughput of the image forming apparatus, it is required to transmit the status information from the option apparatus to the main apparatus with real time and low delay.

(Communications system)
FIG. 2 is a block diagram for explaining an interface between the main device and the optional device in the present embodiment. Here, the option devices 20b and 20c are omitted for the sake of brevity, but the option devices 20b and 20c have the same configuration as the option device 20a.

  Interface signal lines between the control CPU 200 of the main device and the control CPU 210 of the option device 20a are a clock signal line 201, a command signal line 202, and a status signal line 203. The clock signal line 201 is a signal line for transmitting a clock signal from the master device to each slave device. The command signal line 202 is a signal line for transmitting a command signal from the master device to each slave device in synchronization with the clock signal. The status signal line 203 is a status signal line that transmits a status signal indicating the status of the slave device from at least one slave device to the master device in synchronization with the clock signal. The clock signal is called “CLK signal”, the command signal is called “CMD signal”, and the status signal (status signal) is called “STS signal”. The CMD signal is wired so as to be input to the input port 211 for external interrupt. Note that the CMD signal and the STS signal are data signals.

  The control CPU 200 of the main device includes a CLK generation unit 204, a CMD transmission unit 205, and an STS reception unit 206. The CLK generator 204 generates a CLK signal and sends out the clock signal line 201. For example, when the signal level of the status signal line changes for all slave devices connected to the master device, the CLK generation unit 204 sends a CLK signal for causing the slave device to transmit the STS signal to the clock signal line 201. . The CMD transmission unit 205 transmits the CMD signal to the command signal line 202 in synchronization with the CLK signal. The STS receiver 206 receives the STS signal via the status signal line 203 in synchronization with the CLK signal.

  The control CPU 210 of the optional device includes a CLK input unit 214, a CMD reception unit 215, and an STS transmission unit 216. The CLK signal is received via the CLK input unit 214 and the clock signal line 201. The CMD receiver 215 receives a CMD signal via the command signal line 202 in synchronization with the CLK signal. For example, the CMD receiving unit 215 waits to receive a CMD signal via the command signal line when the signal level of the command signal line 202 changes, and synchronizes with the CLK signal when a clock signal is transmitted from the master device. Receive a signal. The STS transmitter 216 transmits the STS signal via the status signal line 203 in synchronization with the CLK signal.

  In this way, the main device functions as a master device that supplies the CLK signal and the CMD signal. The option device 20a operates in response to the CLK signal and the CMD signal supplied from the main body device, and functions as a slave device that outputs the STS signal.

  FIG. 3 is an exemplary functional block diagram of main functions implemented in each control CPU. The transmission unit 301 included in the CMD transmission unit 205 changes the signal level of the command signal line 202 to transmit the transmission of the command signal via the command signal line 202 to each slave device. The detection unit 302 included in the STS reception unit 206 detects that the signal level of the status signal line 203 has changed for all slave devices.

  The detection unit 311 included in the CMD reception unit 215 detects that the signal level of the command signal line 202 connected to the slave device has changed. The notification unit 312 included in the STS transmission unit 216 notifies the master device that preparation for transmitting the STS signal is completed by changing the signal level of the status signal line 203 connected to the slave device.

  The state information transmitting unit 313 transmits the STS signal for transmitting the dependency information to the master device in synchronization with the CLK signal for transmitting the STS signal. Further, the state information transmission unit 313 transmits the STS signal for transmitting the independent information to the master device in synchronization with the CLK signal for receiving the CMD signal. Here, the dependency information is state information that depends on the CMD signal (that is, a response to an explicit inquiry). The non-dependent information is state information that does not depend on the CMD signal (that is, information that is determined to be transmitted in advance even without an inquiry). For example, information that requires real-time properties is preferably processed as independent information. The acquisition unit 314 acquires dependency information, non-dependence information, and the like using a state detection sensor such as a sheet sensor, for example.

  FIG. 4 is a timing chart for explaining a specific example of the serial communication method between the main device and the optional device. Here, communication between the main device and the option device 20a will be described as an example. Of course, communication can be performed in the same manner with respect to the main device and the option device 20b, and the main device and the option device 20c.

  t1 indicates the communication start timing. t2 indicates the switching timing from the command transmission period to the status transmission period. t3 indicates the communication end timing.

  The main device normally maintains the signal level of the CMD signal at the high level, and changes it to the low level at the communication start timing t1. On the other hand, in the option device 20a, a low (edge) level CMD signal is input to the input port 211. This becomes an interrupt signal. The option device 20a detects an interrupt and changes the STS signal to a low level. As a result, the option device 20a shifts to the serial reception mode and prepares to receive the first CMD signal (1st command) 308 among a plurality of options.

  When the reception of the first CMD signal 408 is completed in synchronization with the first CLK signal 404, the option device 20a prepares to receive the second CMD signal (2nd command) 409. When the reception of the second CMD signal 409 is completed in synchronization with the second CLK signal 405, the option device 20a analyzes the content of the command included in the received CMD signal and prepares for status return. Thus, the first CLK signal 404 and the second CLK signal 405 are clock signals for receiving commands.

  When preparation for returning the status is completed (t2), the option device 20a changes the STS signal to the high level and shifts to the serial transmission mode. The option device 20a transmits a first STS signal (1st status) 410 loaded with status as transmission data in synchronization with the third CLK signal 406. Further, the option device 20a transmits a second STS signal (2nd status) 411 in which the status is mounted as transmission data in synchronization with the fourth CLK signal 407. When the transmission of the second STS signal is completed, the option device 20a shifts to the general-purpose port mode by changing the signal level of the STS signal to the Low level. Then, the option device 20a executes the received command and prepares for the next communication. When ready for communication (t3), the option device 20a changes the STS signal to the high level.

  FIG. 5 is a flowchart of serial communication executed in the main device. In step S501, the detection unit 302 of the STS reception unit 206 determines whether or not the STS signal is high. When the STS signal becomes High, the process proceeds to Step S502, and the transmission unit 301 of the CMD transmission unit 205 changes the signal level of the CMD signal to Low.

  In step S503, the CMD transmission unit 205 transmits 1st command. In step S504, the CMD transmission unit 205 transmits 2nd command. In step S505, the detection unit 302 of the STS reception unit 206 determines whether or not the STS signal has changed to High. When the STS signal changes to High, the process proceeds to step S506, where the CLK generating unit 204 sends out the CLK signal, and the STS receiving unit 206 receives 1st status. In step S507, the CLK generation unit 204 transmits a CLK signal, and the STS reception unit 206 receives 2nd status.

  FIG. 6 is a flowchart of serial communication executed in the optional device. In step S601, the detection unit 311 of the CMD reception unit 215 determines whether or not there is an interruption due to changing the CMD signal to Low. If there is an interrupt, the process proceeds to step S602, and the notification unit 312 of the STS transmission unit 216 changes the STS signal to Low. Thereby, the CMD receiving unit 215 waits to receive a command.

  In step S603, the CMD reception unit 215 determines whether reception of the first command is completed. When the reception of the 1st command is completed, the process proceeds to step S604, where the notification unit 312 changes the STS signal to Low, while the CMD reception unit 215 again shifts to the reception wait state. In step S605, the CMD receiving unit 215 determines whether or not the reception of the 2nd command is completed. When the reception of the 2nd command is completed, the process proceeds to step S606, and the CMD receiving unit 215 analyzes the content of the received command.

  In step S607, the status information transmission unit 313 sets a status corresponding to the received command to transmission data in order to prepare 1st status. In step S608, the notification unit 312 changes the STS signal to High, so that the STS transmission unit 216 enters a transmission waiting state. Thereafter, when a clock signal is input, the state information transmission unit 313 transmits 1st status in synchronization with the clock signal. In step S609, the STS transmission unit 216 determines whether or not the transmission of the 1st status is completed.

  When completed, the process proceeds to step S610, and in order to prepare 2nd status, a status corresponding to the received command is set in the transmission data. In step S611, the notification unit 312 changes the STS signal to High, so that the STS transmission unit 216 enters a transmission waiting state. In step S612, the STS transmission unit 216 determines whether transmission of 2nd status is completed. When completed, the process proceeds to step S613, and the notification unit 312 changes the STS signal to Low. In step S614, control CPU 210 executes processing according to the content of the received command. In step S615, the notification unit 312 changes the STS signal to High.

  According to this embodiment, when a slave device transmits data from the slave device to the master device without providing a dedicated line for handshaking by notifying that the STS signal is ready to be transmitted. The handshake can be realized.

  In addition, according to the present embodiment, it does not always wait for a fixed time after receiving a command as in the prior art, and handshaking is executed by an STS signal as soon as processing corresponding to the command is completed. Therefore, the processing efficiency is improved as compared with the conventional case. In general, the processing time for command analysis and command execution differs depending on the content of the command. For this reason, conventionally, standby processing is performed for the assumed maximum processing time, and the process proceeds to the next step. On the other hand, in this embodiment, it is not necessary to always wait for the maximum processing time, so that the time can be reduced.

  In this embodiment, both 1st command and 2nd command are 8 bits, and 1st status and 2nd status are described as 8 bits, but this is only an example. The command may be divided into two pieces of data having a 16-bit length without being divided into two. The status is the same. Command reception and status transmission are separated on the time axis, but this is only an example. You may apply the handshake which concerns on this invention with respect to the system which transmits and receives a command and status in parallel.

  The master device may transmit to each slave device that the command signal is transmitted via the command signal line by changing the signal level of the command signal line. Thereby, it is possible to realize handshaking when data is transmitted from the master device to the slave device without providing a dedicated line for handshaking.

[Embodiment 2]
The second embodiment also relates to communication between the image forming apparatus and the optional apparatus, as in the first embodiment. In the first embodiment, when one optional device is connected to one main device, handshaking is realized without newly providing a signal line dedicated to handshaking. On the other hand, in the second embodiment, when a plurality of option devices are connected to one main device, the handshake is realized without newly providing a signal line dedicated for handshaking between each option device and the main device. A method will be described. In the following, description of the same parts as those in the first embodiment will be omitted, and description will be made focusing on characteristic parts of the present embodiment.

  Specifically, the STS signal lines of a plurality of option devices are connected in a high OR wired OR format. A wired OR (logical OR connection) is a logic circuit in which the output becomes High when all the input signals become High, but the output becomes Low if even one of the input signals is Low. It should be noted that the wired OR actually functions as an AND. That is, the wired OR is like an AND element with N (natural number of 2 or more) input and 1 output.

  For example, each option device sets the STS signal to High when preparation for transmission or reception is completed. When all the STS signals from the option devices become High, the STS signal input to the main device also becomes High. That is, the fact that the STS signal input to the main unit becomes High means that the handshake of all the optional devices has been completed.

  FIG. 7 is a block diagram for explaining an interface between the main device and the optional device according to the second embodiment. The internal configuration of the control CPUs 220 and 230 is the same as that of the control CPU 210 shown in FIGS.

  As shown in FIG. 7, status signal lines 203 are connected to branch lines 701, 702, and 703 of status signal lines extending from each option device by wired OR. The AND elements 711 and 712 function as logical sum connection means for logically connecting the branch lines of the status signal lines extending from the respective slave devices to the detection unit 302. The AND elements 711 and 712 are merely conceptual, and are realized by preferable circuit elements well known in actual circuit design. The STS signal (STS_in) input to the main device is a wired OR output of the STS signals (STS_out1, STS_out2, STS_out3) of each option device. If STS_out1, STS_out2, and STS_out3 all become High, STS_in also becomes High.

  FIG. 8 is a timing chart for explaining a specific example of the serial communication method between the main device and each optional device. In this example, it is assumed that a command specifying the option device 20c is transmitted and the option device 20c returns a status.

  t11 indicates the communication start timing. t12 indicates the timing when the handshake of all the optional devices is completed. t13 indicates the communication end timing. The main device holds the signal level of the command signal line 202 at the high level before the start of communication, and changes to the low level when the communication start timing (t11) arrives.

  On the other hand, each of the option devices 20a, 20b, and 20c sets the STS signal to Low by the interruption by the command signal line 202, and shifts to the serial reception mode. Each optional device receives the first and second CMD signals 808 and 809 in synchronization with the CLK signals 804 and 805, and analyzes the contents of the command. Each optional device prepares an STS signal according to the analyzed contents.

  Here, each CMD signal includes designation information for designating an optional device to execute a command (to return a status). The designation information is identification information assigned to each option device. Therefore, each optional device determines whether or not it is designated. Here, it is assumed that the option device 20c is designated.

  Since the option devices 20a and 20b are not specified, FFh is set as transmission data. FFh is all 1 (all High) in binary number, but this is because the branch of the status signal line is connected by wired OR. On the other hand, since the option device 20c is specified, the option device 20c creates an STS signal (1st status) 817 in which a status corresponding to the command is set. Similarly, an STS signal (2nd status) 818 is also prepared.

  When the preparation for transmitting the STS signal is completed, each option device switches the STS signals (STS_out1, STS_out2, STS_out3) to the high level and maintains them. Thereby, each optional device shifts to the serial transmission mode. The status signal line 203 employs a wired OR type connection. Therefore, when all the STS signals (STS_out1, STS_out2, STS_out3) become High, the STS signal (STS_in) to the master device becomes High (t12).

  Thereafter, in synchronization with the CLK signal 806, the option device 20a / 20b outputs FFh to the status signal line. Also, the option device 20c transmits 1st status (817). Similarly, in synchronization with the CLK signal 807, the option device 20a / 20b outputs FFh to the status signal line. Further, the option device 20c transmits 2nd status (818).

  The STS_out1 to STS_out3 signals are connected in a wired OR format. Therefore, 1st status (817) and 2nd status (818) are reflected in STS_in, and become 1st status (810) and 2nd status (811), respectively.

  Each option device 20a, 20b, 20c sets the STS signal to the Low level and shifts to the general-purpose port mode. Only the designated option device 20c executes the command. When each optional device is ready for communication, the STS signal is changed to the high level again to shift to the general-purpose port mode. Due to the wired OR connection, when all the STS signals become High, the STS signal to the master device becomes High again (t13). Thereby, the master device recognizes that all the optional devices are ready for communication.

  As described above, in this embodiment, even when a plurality of slave devices are connected to one master device, data is transmitted from the slave device to the master device without providing a dedicated line for handshaking. A handshake can be realized. Conventionally, since the maximum processing time among the processing times of a plurality of optional devices is set as a common waiting time, the efficiency is low. However, according to the present embodiment, each option device can be made by handshaking as soon as the processing is completed and proceeding to the next communication step, so that the processing time can be shortened.

  Further, by employing a logical OR connection means such as a wired OR for connection of signal lines, there is an advantage that the technical idea of the present invention can be easily applied to an image forming apparatus in which the number of optional devices increases or decreases.

[Embodiment 3]
Hereinafter, Embodiment 3 according to the present invention will be described. The third embodiment also relates to communication between the image forming apparatus and the optional apparatus, as in the first and second embodiments. Therefore, below, description is abbreviate | omitted about the part similar to Embodiment 1, 2, and it demonstrates focusing on the characteristic part of this embodiment.

  In an image forming apparatus to which a plurality of option devices are connected, in order to improve the throughput (the number of prints per unit time) of the entire device, it is desirable to monitor the sheet conveyance state of each option device in real time. For example, when the sensor state is individually inquired with respect to each option device, the time until the information of each option device is updated becomes longer, so the real-time property of the information is likely to be lost. This makes it difficult to control the sheet conveyance appropriately.

  Therefore, the present embodiment makes it possible to acquire necessary information regarding the optional device in real time without transmitting a status request command. As a result, the main device can monitor the status information of all the optional devices without losing real-time characteristics.

  Specifically, in parallel with the reception of the CMD signal from the master device (in synchronization with the clock signal for receiving the CMD signal), each slave device converts the information required for real-time property into the STS signal. Install and send. As a result, the master device can obtain information required for real-time performance from each slave device without sending an inquiry.

  FIG. 9 is a timing chart for explaining a specific example of a serial communication method between the main device and each optional device. In addition, the same reference numerals are given to portions common to FIG.

  When there is an interrupt by the CMD signal (t11), each optional device shifts to the serial transmission / reception mode by switching the STS signal to the low level. Furthermore, each optional device acquires and determines state information (eg, information on a paper presence sensor or a conveyance sensor) that requires real-time properties. Thereby, it becomes easy to ensure real time property.

  Each option device sets the determined state information as transmission data. Bit positions (transmission period) that can be used by each optional device to transmit status information are different. According to FIG. 9, the status information of each option device is 2 bits. Of the two bits, the first bit can be used as the detection result of the paper presence sensor, and the second bit can be used as the detection result of the transport sensor. According to FIG. 9, the STS signals that carry the status information of the option device 20a are 921 and 922. STS signals 923 and 924 for carrying status information of the option device 20b are shown. STS signals that carry status information of the option device 20c are 925 and 926, respectively. Each STS signal is transmitted in synchronization with the CLK signals 804 and 805. The content of the bit is, for example, High when there is no paper and Low when there is paper.

  Finally, the STS signals from the optional devices are combined by wired OR to become one STS signal 919, 920. Each option device outputs High at a bit position other than the bit position at which it transmits state information. This is a measure for adopting wired OR.

  Each option device changes the STS signal to Low once transmission of the first STS signal is completed. This is to wait for the second CMD signal 809. Moreover, Low of the STS signal means transition to the serial transmission / reception mode. Each optional device prepares for transmission of the second STS signal 922, 924, 926. That is, each optional device acquires state information that requires real-time performance.

  Here, the state information transmitted first and the state information transmitted second may be the same. The STS receiver of the main device adopts the status information received from the option device for the first time and the status information received from the option device for the second time, and adopts it if they are different. Thereby, there is an advantage that an error due to noise or the like generated at the time of transmission / reception of state information can be removed.

  As described above, the status information transmission unit 313 of each option device performs non-transmission at different transmission timings among a plurality of transmission timings obtained by dividing a transmission period (for example, an 8-bit transmission period) for the same CLK signal. Dependency information status signal is transmitted. On the other hand, the state information transmission unit 313 provided in the slave device specified by the command signal transmits STS signals 817 and 818 for transmitting the dependency information. Then, the state information transmission unit 313 provided in the slave device not designated by the command signal maintains the signal level of the status signal line at a high level.

  In addition, when the signal level of the command signal line 202 changes, the acquisition unit 314 determines at least one of dependency information and non-dependency information. As described above, the dependency information is state information that depends on the CMD signal, and the non-dependence information is state information that does not depend on the CMD signal.

  FIG. 10 is a flowchart for processing of the main device. In addition, about the process demonstrated in FIG. 5, description is abbreviate | omitted by attaching | subjecting the same reference number. Subsequent to steps S501 and S502, step S1001 is executed.

  In step S1001, the control CPU 200 determines whether transmission of the first command is completed and reception of the STS signal 919 from the option devices 20a, 20b, and 20c is completed. When both are completed, the process proceeds to step S1002, and the control CPU 200 determines whether transmission of the 2nd command is completed and reception of the STS signal 920 from each option device is completed. When both are completed, the process proceeds to step S1003.

  In step S1003, the control CPU 200 compares the first STS signal 919 and the second STS signal 920 to determine whether or not they are the same. If they are the same, the process proceeds to step S1004, and the control CPU 200 updates the status information of each option device held in a storage device (not shown) to the received status information. On the other hand, if they are not the same, the process proceeds to step S505 without updating the state information. Thereafter, S505 to S507 are executed.

  FIG. 11 is a flowchart for processing of the optional device. The processes described in FIG. 6 are denoted by the same reference numerals, and the description thereof is omitted. Steps S602 to S605 are replaced with S1101 to S1107.

  In step S <b> 1101, the acquisition unit 314 of each option device acquires status information from a paper presence sensor, a paper transport sensor, and the like to determine the content. In step S1102, the status information transmission unit 313 of each option device sets the first status information as transmission data, and generates STS signals 921, 923, and 925.

  In step S1103, the notification unit 312 of each option device changes the STS signal to Low. In step S1104, the control CPU of each option device receives 1st command and determines whether transmission of the first status information is completed. If both are completed, the process proceeds to step S1105. In step S1105, the status information transmission unit 313 of each option device sets the second status information as transmission data, and generates STS signals 922, 924, and 926. In the case of transmitting a status signal having the same contents a plurality of times from the viewpoint of error suppression, the second status information is the same as the first status information.

  In step S1106, the notification unit 312 of each option device changes the STS signal to Low. In step S1107, the control CPU of each option device receives the 2nd command and determines whether or not the transmission of the second state information has been completed. If both are completed, steps S606 to S615 described above are executed.

  As described above, according to the present embodiment, in parallel with receiving the CMD signal from the master device (in synchronization with the clock signal for receiving the CMD signal), each slave device has real-time characteristics. The requested information is transmitted in the STS signal. As a result, the master device can obtain information required for real-time performance from each slave device without sending an inquiry. Therefore, the image forming apparatus can easily improve the throughput. Other effects are as described in the first and second embodiments.

1 is an overall configuration diagram of an image forming apparatus applied in common to each embodiment. It is a block diagram for demonstrating the interface of the main body apparatus and option apparatus in this embodiment. It is an example functional block diagram about the main functions mounted in each control CPU. It is a timing chart for demonstrating the specific example of the serial communication system of a main body apparatus and an option apparatus. It is a flowchart about the serial communication performed in a main body apparatus. It is a flowchart about the serial communication performed in an option apparatus. FIG. 9 is a block diagram for explaining an interface between a main device and an optional device in the second embodiment. It is a timing chart for demonstrating the specific example of the serial communication system of a main body apparatus and each option apparatus. It is a timing chart for demonstrating the specific example of the serial communication system of a main body apparatus and each option apparatus. It is a flowchart about the process of a main body apparatus. It is a flowchart about the process of an option apparatus.

Claims (9)

Master device and multiple slave devices can be connected,
A clock signal line for transmitting a clock signal from the master device to the plurality of slave devices;
A command signal line for transmitting a command signal from the master device to the plurality of slave devices in synchronization with the clock signal;
A status signal line for transmitting a status signal representing its own state from at least one slave device of the plurality of slave devices to the master device in synchronization with the clock signal;
A notification means provided in the slave device for notifying that the status signal is ready to be transmitted by switching the signal level of the status signal line from the first level to the second level;
A detection unit that is provided in the master device and detects that the signal level of the status signal line transmitted from the notification unit included in the slave device has reached the second level;
All of the plurality of slave devices, after receiving the command signal from the master device, whether or not receiving an instruction to return a status signal by the command signal, when the preparation for transmission of the status signal is completed, Switching the signal level of the status signal line to the second level;
After the master device has transmitted the command signal to all of the plurality of slave devices, the signal level of the status signal line has reached the second level for all of the plurality of slave devices by the detecting means. When detected, the serial communication system controls to transmit the clock signal for transmitting the status signal to all of the plurality of slave devices. When the command signal is received from the master device, the slave device requested to transmit the status signal to the master device by the command signal among the plurality of slave devices is synchronized with the clock signal. Send
The slave device that is not requested to transmit the status signal to the master device by the command signal transmits the status signal from the slave device that is requested to transmit the status signal to the master device. The serial communication system according to claim 1, wherein the signal level of the status signal line is switched to the second level for the purpose.   3. The serial communication according to claim 1, wherein the plurality of slave devices further include a logical sum connection unit for logically connecting a status signal line of the slave device and a status signal line of another slave device. system.   4. The serial communication system according to claim 1, wherein the plurality of slave devices transmit a status signal having the same content a plurality of times in synchronization with the clock signal. 5.   3. The serial communication system according to claim 1, wherein the first level of the status signal line is a low level, and the second level is a high level. 4. Master device and multiple slave devices can be connected,
A clock signal line for transmitting a clock signal from the master device to the plurality of slave devices;
A command signal line for transmitting a command signal from the master device to the plurality of slave devices in synchronization with the clock signal;
A status signal line that transmits a status signal representing its state from at least one slave device of the plurality of slave devices to the master device in synchronization with the clock signal, and a serial communication system comprising:
The slave device, after receiving the command signal, a first transmission for transmitting a first status signal to the master device in synchronization with the clock signal for transmitting the status signal;
Serial communication characterized in that second transmission is performed in which a second status signal different from the first status signal is transmitted to the master device in synchronization with the clock signal for receiving the command signal. system. The slave device acquires dependency information that depends on the command signal and non-dependency information that does not depend on the command signal among statuses representing its state,
The serial communication system according to claim 6, wherein the dependence information is transmitted to the master device as the first status signal, and the non-dependence information is transmitted to the master device as the second status signal. . A clock signal line for receiving a clock signal from the master device;
A command signal line for receiving a command signal from the master device in synchronization with the clock signal;
A status signal line that transmits a status signal representing its own state to the master device in synchronization with the clock signal, and a slave device comprising:
Notification means for notifying the master device that the slave device is ready to transmit the status signal by switching the signal level of the status signal line from the first level to the second level;
When transmission of the status signal is requested to the master device by the command signal , after the signal level of the status signal line is switched to the second level, the status signal line is synchronized with the clock signal. To send the status signal,
If the command signal does not request transmission of the status signal to the master device, the status signal from the other slave device requested to transmit the status signal to the master device is transmitted to the master device. A slave device, wherein the signal level of the status signal line is switched to the second level for transmission. A clock signal line for receiving a clock signal from the master device;
A command signal line for receiving a command signal from the master device in synchronization with the clock signal;
A status signal line that transmits a status signal representing its own state to the master device in synchronization with the clock signal, and a slave device comprising:
The slave device, after receiving the command signal, a first transmission for transmitting a first status signal to the master device in synchronization with the clock signal for transmitting the status signal;
Wherein in synchronization with the clock signal for receiving a command signal, according to claim 8, wherein the second status signal different from the first status signal to perform a second transmission to be transmitted to the master device The slave device described in 1 .

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