JPH08237236A - Image forming system and image forming device and data transfer control method - Google Patents

Abstract

PURPOSE: To output a response signal to a connected host computer at optimized timing by changing the value of communication control timing whenever data is transferred from the host computer and outputting the response signal until a termination notice is received. CONSTITUTION: The host computer 10 transfers data of FFh to a printer and the printer waits for an nACK signal pulse being a response showing that data is received for HTMAX time which is previously stored in a response waiting maximum time register 14. When the nACK signal pulse cannot be detected during the standby, data of FFh is transferred to the printer again and the operation is repeated until the nACK signal pulse is detected. When the nACK signal pulse is detected, data of 55h is transferred to the printer and a processing is terminated. The printer delays the output timing of the nACK signal pulse whenver data is received and sets atim-time at receiving data of 55h to be the timing at transferring data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming system, an image forming apparatus and a data transfer control method, and in particular, data between a host computer (host apparatus) and a printer (image forming apparatus) connected via a Centronics interface. The present invention relates to an image forming system, an image forming apparatus, and a data transfer control method for adjusting communication control timing in order to perform transfer at high speed.

[0002]

2. Description of the Related Art Conventionally, data transfer between a host computer and a printer, which are connected by a Centronics interface, is performed by nStrobe signal (output from host) and nAC.
The handshake of the K signal (printer output) is used. The nACK signal means that the printer has received data, and the host computer starts preparation for the next data transfer by receiving this signal, so the timing of outputting the nACK signal pulse affects the data transfer rate. Conventionally, the timing at which the printer outputs the nACK signal pulse is fixed or variable in several steps.

[0003]

However, the above-mentioned conventional example has the following problems.

First, the performance of the Centronics interface of the host computer connected to the printer is diverse, so that the printer can nACK at an early timing.
When a signal pulse is output, the nA will be output to the host computer equipped with a low-performance Centronics interface.
It is possible that the CK signal pulse will not be recognized.

Therefore, if the timing for outputting the nACK signal pulse of the printer is fixed, it is necessary to output the nACK pulse at a late timing in accordance with the host computer equipped with a low-performance Centronics interface. The data transfer rate remains low even when connected to a transferable host computer.

Further, even when the timing of outputting the nACK signal pulse of the printer is variable in several steps (for example, two steps of high speed / low speed), the timing of outputting the nACK signal pulse can be variously connected to the printer. It was practically impossible to optimize the performance of the host computer.

The present invention has been made in view of the above points, and an object thereof is to provide an image forming apparatus (a host computer or the like) for outputting image information via a Centronics interface ( (Such as a printer) can output the nACK signal pulse to the host device at a timing optimized for the performance of the Centronics interface, which allows the user to operate the communication control timing directly without high speed. An object of the present invention is to provide an image forming system, an image forming apparatus, and a data transfer control method that enable data transfer.

[0008]

In order to achieve the above object, an image forming system of the present invention comprises a host apparatus for outputting image information, a Centronics interface, and an image forming apparatus connected to the host apparatus via the Centronics interface. An image forming system including a device, a nACK signal pulse which is a response in which a predetermined first data is transferred after a communication control timing command is issued to the image forming device and the image forming device receives the data. For a predetermined time, and when the nACK signal pulse cannot be detected within the predetermined time, the first data is transferred again to the image forming apparatus, and these operations are repeated until the nACK signal pulse is detected. When the nACK signal pulse is detected, the predetermined second data is transferred to the image forming apparatus to adjust the communication control timing. And a host device to end the process, after receiving the communication control timing command, receives data from the host device, until receiving the second data, the each receive a transfer of the first data nAC
The image forming apparatus is characterized in that the timing of outputting the K signal pulse is delayed and the timing time at the time of receiving the second data is used as the communication control timing at the time of transferring the image information data.

Further, in the image forming apparatus of the present invention, in the image forming apparatus connected to the host apparatus via the Centronics interface, a signal such as image information is received from the host apparatus via the Centronics interface and a response signal is transmitted. Communication means, and a flag setting means for setting a communication control timing adjustment flag indicating that the communication control timing of the Centronics interface is being adjusted in response to receiving a communication control timing adjustment command issued by the host device; When the communication control timing adjustment flag is set, nA which is a response signal each time data is received from the host device.
The timing of outputting the CK signal pulse is changed to set the nAC to the shortest timing that can be recognized by the host device.
An output timing adjusting means for adjusting the communication control timing so as to output a K signal pulse, and a storage means for storing the value of the communication control timing adjusted by the output timing adjusting means are provided. .

Further, as an aspect of the image forming apparatus of the present invention, the communication control timing of the communication means is variable according to the value of the communication control timing stored in the storage means. can do.

As another form of the image forming apparatus of the present invention, the host device performs communication control indicating that the communication control timing of the Centronics interface is being adjusted after the communication control timing adjustment command is issued. It has a flag setting means for setting a timing adjustment flag, and outputs a signal indicating that the nACK signal pulse has been detected to the image forming apparatus and resets the communication control timing adjustment flag. be able to.

Further, the data transfer control method of the present invention is the data of an image forming system including a host device for outputting image information, a centronics interface, and an image forming device connected to the host device via the centronics interface. In the transfer control method, the host apparatus issues a communication control timing command to the image forming apparatus, and the image forming apparatus receiving the communication control timing command causes the image forming apparatus to receive an nSTR from the host apparatus.
A procedure for changing the timing of outputting the nACK signal pulse, which is a response signal, from the falling edge or the rising edge of the OBE signal by delaying each time from the shortest time for each data transfer;
When the host device recognizes the nACK signal pulse, it outputs a recognition signal indicating that the nACK signal pulse has been recognized, and the shortest timing recognized by the host device in response to the recognition signal received by the image forming device. Is set as the output timing of the nACK signal pulse at the time of data transfer of the image signal.

[0013]

According to the present invention, after the printer connected through the Centronics interface sets the communication control timing adjustment flag, communication control is performed every time data is transferred from the host computer until the end notification 55h of data is received. NAC by changing the timing value
The K signal pulse is output and the nACK signal pulse can be output to the connected host computer at an optimized timing, so that the user does not have to manually operate the communication control timing directly, but high-speed data transfer is possible. It can be performed.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows the overall construction of an embodiment to which the present invention is applied. In the figure, 10 is a host computer, 20 is a printer, and 30 is a Centronics interface cable. The host computer 10 includes an operating system (OS), application software (AP), and the like, and has a function of transferring print data, print commands, and the like to the printer 20 via the Centronics interface 30, and expanding and printing image data. Have. On the other hand, the printer 20 has a function of expanding print data, print commands, and the like sent from the host computer 10 into image data, forming a permanent visible image on a recording sheet, and outputting the image. Here, the print data means data composed of a character code and a control code, for example, PDL (page description language).
Or PJL (print job language) data.

The printer 20 may of course be a color printer that forms and outputs a color permanent visible image.

The block diagram of FIG. 2 shows an example of a detailed configuration of the host computer 10 of FIG. 1 of the present embodiment. The host computer 10 has a memory containing software such as an operating system, application software, and device drivers, and these software sends print data and print commands to the printer to develop and print image data. In the configuration of this example, the device driver is the printer driver 12 that is compatible with the printer 20. The printer driver 12 includes a communication control timing adjustment flag 13 indicating that the communication control timing is being adjusted, and a response waiting maximum time register 14 that holds the maximum time to wait for the nACK signal pulse output from the printer 20. The host computer 10 also includes a Centronics interface 11 that transfers data to the printer 20.

The block diagram of FIG. 3 shows an example of a detailed configuration of the printer 20 of FIG. 1 of the present embodiment. The printer 20
A control system is composed of a microprocessor system including ROM, RAM (both not shown), etc., and each block described below is connected by a bus 29. That is, the printer 20 analyzes the print data and print commands sent from the host computer 10, the control unit 22 that controls the entire printer 20, and the Centronics interface 21 that sends and receives signals to and from the host computer 10 through the Centronics interface cable 30. Command analysis unit 23, printer engine 24 that forms a permanent visible image on recording paper, expansion memory 25 that expands image data into a bitmap, communication control timing adjustment flag 26 that indicates that communication control timing is being adjusted, host computer 10 A host response time register 27 that holds the timing of outputting the nACK signal pulse, a timer unit 28 that provides time information for managing the timing of outputting the signal, and a bus 29 are provided.

FIG. 4 shows an example of a command issued by the printer driver 12 of the host computer 10 of FIG. 2 of this embodiment. The communication control timing adjustment command shown in the figure includes a command number for identifying the command.

The timing chart of FIG. 5 shows the timing of data transfer when a general Centronics interface is used as the Centronics interface 11 of FIG. 2 and the Centronics interface 21 of FIG. Here, the DATA signal is the host computer 1
The data 0 is output and is transferred to the printer 20. This DATA signal is composed of 8 bits. nST
The ROBE signal means that the host computer 10 outputs the data to the printer 20 at low level zero LO (0). The BUSY signal is output by the printer 20 and means that new data cannot be accepted at the high level 1 HI (1).

The nACK signal means that the printer 20 outputs and receives data at LO (0) of low level zero.

As shown in FIG. 5, first, at time t1, the host computer 10 transfers the data to be transferred to the printer 20 to D
Output with ATA signal. At the next time t2, the host computer 10 changes the output of the nSTROBE signal from HI (1) to LO (0) to notify the printer 20 that the data has been output.

At the next time t3, the printer 20 changes the output of the BUSY signal from LO (0) to HI (1) to notify that new data cannot be received.

At the next time t4, the host computer 10 changes the output of the nSTROBE signal from LO (0) to HI (1).
By setting, the end of data output is notified.

At the next time t5, the printer 20 changes the output of the nACK signal from HI (1) to LO (0) to notify the host computer 10 that the data has been received. At the next time t6, the printer 20 outputs the BUSY signal to HI.
By changing from (1) to LO (0), it is notified that new data can be accepted. At the next time t7, the printer 20 outputs the nACK signal from LO (0) to HI (1).
By doing so, the host computer 10 is notified of the completion of data reception.

With the above operation, 8-bit (1 byte) data transfer is completed. Here, from time t2 to time t5
The time until is taken as the variable atim.

The flowchart of FIG. 6 shows an example of the processing procedure of this embodiment. In particular, the printer driver 12 of the host computer 10 issues the communication control timing adjustment command of FIG. 4 to the printer 20, and the printer that receives the command changes the timing of outputting the nACK signal pulse of FIG. Shows a processing procedure until adjustment so as to output the nACK signal pulse at the shortest timing that can be recognized.

Specifically, this adjustment is performed at the timing t5 at which the nACK signal pulse, which is the response of the printer 20, is output from the time t2 when the nSTROBE signal output from the host computer 10 falls (HI → LO) in FIG.
Is delayed from the shortest for each data transfer, and the shortest timing at which the host computer 10 recognizes the nACK signal pulse is set as the nACK signal pulse output timing of the data transfer. Note that the processing of FIG. 6 is processed in the host computer 10 according to the programs of the operating system, applications, and printer driver incorporated therein. In the printer 20, the control unit 22 executes the program according to the program stored in the built-in memory.

In the flowchart of FIG. 6, step S1 is an initialization process of the printer 20 and the host computer 10. When the power is turned on, the printer 20 can receive the print data and the print command transferred from the host computer 10. Then, the process proceeds to step S2.

In step S2, the host computer 10 issues the communication control timing adjustment command shown in FIG. 4, and proceeds to step S3.

In step S3, the printer 20 receives the communication control timing adjustment command issued by the host computer 10 in step S2 via the Centronics interface 21, analyzes this command by the command analysis section 23, and proceeds to step S4.

In step S4, the host computer 1
0 and the printer 20 perform a communication control timing adjustment process described later with reference to FIGS. 7 and 8, and the present process ends.

The flow chart of FIG. 7 shows an example of the processing performed by the host computer in the communication control timing adjustment processing in step S4 of FIG. In this flowchart, the host computer 10 sends a message to the printer 20.
Data of Fh (h indicates a hexadecimal number, the same applies hereinafter) is transferred, and an nACK signal pulse, which is a response to the printer 20 receiving the data, sends a response wait maximum time register 14
If the nACK signal pulse cannot be detected during the waiting for the HTMAX time stored in advance in the above, the data of FFh is transferred again to the printer 20, and this operation is repeated until the nACK signal pulse is detected. , NACK signal pulse is detected, data of 55h is transferred to the printer 20 and the process is terminated. The detailed timing of data transfer between the host computer 10 and the printer 20 at this time is the same as that shown in FIG.

Next, the details will be described. The series of processes described below are all performed by the host computer 10. In FIG. 7, the communication control timing adjustment flag 1 of the printer driver 12 in step S10.
Set 3 to 1. Communication control timing adjustment flag 1
When 3 is set to 1, the printer driver 12 does not accept a print data transfer request from the operating system or application software in the host computer 10, and executes the communication control timing adjustment process. Then, the process proceeds to step S11.

In step S11, a variable hti indicating time
Clear m to 0. This htim is a timer variable managed by the operating system and counts up at regular time intervals. Then, the process proceeds to step S12. In step S12, the operating system timer is started. As a result, the variable htim is incremented by 1 every fixed time. Then step S
Proceed to 13. In step S13, the printer 20 is FFh
Data is transferred and the process proceeds to step S14.

In step S14, the state of the nACK signal of the Centronics interface 11 (HI or LO)
Is checked and the process proceeds to step S15. In step S15, if the nACK signal checked in step S14 is LO (0) (in the case of pulse detection), the process proceeds to step S18.

In step S15, if the nACK signal checked in step S14 is HI (1), the process proceeds to step S16. In step S16, the timer variable htim managed by the operating system is read (read), and the process proceeds to step S17. Step S1
In step S7, if the variable htim read in step S16 is equal to or less than the specified value HTMAX representing the maximum response waiting time, the process returns to step S14.

In step S17, when htim read in step S16 is larger than HTMAX, the maximum response waiting time is exceeded, and the process returns to step S11. Here, it is assumed that the value of HTMAX is preset in the response waiting maximum time register 14 of the printer driver 12.

In step S18, the data of 55h is transferred to the printer 20, and the process proceeds to step S19. here,
Data transfer of 55h to the printer 20 means completion notification of the communication control timing adjustment processing.

In step S19, the communication control timing adjustment flag 13 is reset to 0, and the process ends.

The flowchart of FIG. 8 shows an example of the process performed by the printer 20 in the communication control timing adjustment process in step S4 of FIG. In this flowchart, the control unit 22 of the printer 20 controls the interface signal of the Centronics interface 21 to receive data from the host computer 10,
Is a timing for outputting an nACK signal pulse each time data is received (variable a until receiving 55h data).
This is a time indicated by tim, which is held in the host response time register 27), and indicates the processing until the atim time is set as the communication control timing for data transfer at the time of data reception of 55h. .

The series of processes described below are all performed by the printer 20.

In FIG. 8, the communication control timing adjustment flag 26 of the printer 20 is set to 1 in step S20. When the communication control timing adjustment flag 26 is set to 1, the printer 20 does not treat the data transferred from the host computer 10 as print data and performs the communication control timing adjustment process without expanding the data into image data. Then, the process proceeds to step S21. In step S21,
The timing time atim for outputting the nACK signal pulse held in the host response time register 27 is set to the minimum output time AMIN of the nACK signal pulse, and the process proceeds to the next step S22. Here, AMIN indicates the minimum time for which the Centronics interface 21 of the printer 20 outputs the nACK signal pulse, and the control unit 22 is set in advance.
Is the value held in.

In step S22, the control unit 22 checks the state (HI or LO) of the nSTROBE signal of the Centronics interface 21, and proceeds to the next step S23. In step S23, the nST checked in step S22
If the ROBE signal is HI (1), the trailing edge of the nSTROBE signal has not been detected, so step S22
Return to processing.

In step S23, if the nSTROBE signal checked in step S22 is LO (0), nSTR
Since the fall of the OBE signal has been detected, the process proceeds to the next step S24. In step S24, the control unit 22 takes in the data of the data bus of the Centronics interface 21, and proceeds to the next step S25. In step S25, the control unit 22 executes nSTROB in step S22.
After detecting LO (0) of E signal, nAC after atim time
A K signal pulse is output and the process proceeds to the next step S26.

If the data fetched in step S24 is 55h in step S26, the process proceeds to step S27, in which the communication control timing adjustment flag 26 of the printer 20 is reset to 0, and the process ends.

In step S26, if the data fetched in step S24 is other than 55h, step S28
Proceed to. In step S28, 1 is added to the variable atim, the process returns to step S22, and the processes from step S22 are repeated until the data of 55h is detected.

As described above, according to the present embodiment, the timing of the communication control of the printer is adjusted / optimized for the Centronics interface of various host computers without requiring the operation of the operator of the host computer or the printer. It becomes possible to perform high-speed data transfer.

(Other Embodiments) In the above-described first embodiment of the present invention, the timing atim at which the printer 20 outputs the nACK signal pulse is based on the trailing edge of the nSTROBE signal output by the host computer 10 (FIG. 8). See step S23). However, the timing of outputting the nACK signal pulse may be based on the rising edge of nSTROBE. This will be described as a second embodiment of the present invention. FIG. 9 shows the timing atim2 at which the nACK signal pulse is output in this embodiment.

The flowchart of FIG. 10 shows the process performed by the printer 20 in the communication control timing adjustment process shown in step S4 of FIG. 6 in this embodiment. This flowchart shows that the control unit 22 of the printer 20 controls the interface signal of the Centronics interface 21 to receive data from the host computer 10, and the printer 20 receives an nACK signal pulse for each data transfer until it receives the data of 55h. Is delayed (the time indicated by the variable atim2, which is held in the host response time register 27).
The process until the communication control timing for data transfer is set to atim2 time at the time of receiving data for 5 h is shown. The series of processes described below are all performed by the printer 20.

In FIG. 10, the communication control timing adjustment flag 26 of the printer 20 is set to 1 in step S30. When the communication control timing adjustment flag 26 is set to 1, the printer 20 does not treat the data transferred from the host computer 10 as print data,
The communication control timing adjustment processing is performed without expanding the image data. Then, the process proceeds to step S31. Step S31
Then, the timing atim2 for outputting the nACK signal pulse held in the host response time register 27 is set to the minimum time AMIN of the nACK signal pulse, and the process proceeds to the next step S32. Here, AMIN indicates the minimum time for which the Centronics interface 21 of the printer 20 outputs the nACK signal pulse, and is a value held in the control unit 22 in advance.

In step S32, the control unit 22 checks the state (HI or LO) of the nSTROBE signal of the Centronics interface 21, and proceeds to the next step S33. In step S33, the nST checked in step S32
If the ROBE signal is HI (1), the trailing edge of the nSTROBE signal has not been detected, and thus step S32 is performed.
Return to processing.

In step S33, if the nSTROBE signal checked in step S32 is LO (0), nSTR
Since the falling edge of the OBE signal has been detected, step S34
Go to processing.

In step S34, the control unit 22 fetches the data on the data bus of the Centronics interface 21, and proceeds to the next step S35.

In step S35, the control unit 22 checks the state (HI or LO) of the nSTROBE signal of the Centronics interface 21, and proceeds to the next step S36. In step S36, the nST checked in step S35
If the ROBE signal is LO (0), the process returns to step S35.

In step S36, if the nSTROBE signal checked in step S35 is HI (1), nSTR
Since the rise of the OBE signal is detected, the process proceeds to the next step S37. After detecting HI (1) of the nSTROBE signal in step S35 in step S37, the control unit 22 outputs the nACK signal pulse 2 hours after atim (see FIG. 9), and proceeds to step S38.

In step S38, if the data fetched in step S34 is 55h, the process proceeds to step S39, in step S39 the communication control timing adjustment flag 26 of the printer 20 is reset to 0, and the process ends.

If the data fetched in step S34 is other than 55h in step S38, the process proceeds to step S40, and in step S40, the variable atim2 is incremented by 1. Next, returning to step S32, the processing from step S32 is repeated until the data of 55h is detected.

In the above embodiment, step S in FIG.
27 (or step S39 of FIG. 10), the variable atim (or atim2) after receiving the data of 55h.
8 is sequentially stored in the internal memory of the printer in correspondence with the identification number of the host computer 10 in communication, and then, at the next communication from the same host computer 10, step S21 (or FIG. 10) of FIG. Step S
In step 31), the corresponding data of atim stored in the memory is read and replaced with the above AMIN, and the variable at
By substituting it into im (or atim2), the generation timing of the nACK signal pulse of the printer 20 can be optimized from the beginning, and thus 2
The time for the communication control timing adjustment process from the first time can be shortened.

In this case, the Centronics interface 11 of one of the host computers 10 may be updated to a new model of higher speed, but FIG. 8 (or FIG. 8) in which the attim data stored in the memory is not used. By configuring the process of 10) to be executed each time the update is performed, or at an appropriate fixed number of times of communication, or periodically, it is possible to appropriately deal with the update.

[0061]

As described above, according to the present invention,
When the printer connected by the Centronics interface has the communication control timing adjustment flag set, it changes the communication control timing value each time it receives data transfer from the host computer and outputs an nACK signal pulse until it receives an end notification. As a result, nAC is performed at a timing optimized for the connected host computer.
Since the K pulse can be output, there is an effect that the user can perform high-speed data transfer without directly operating the communication control timing manually.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration example of an image forming system according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a detailed configuration example of a host computer 10 according to an embodiment of the present invention.

FIG. 3 is a block diagram illustrating a detailed configuration example of a printer 20 according to an exemplary embodiment of the present invention.

FIG. 4 is an explanatory diagram showing an example of a communication control timing adjustment command according to an embodiment of the present invention.

FIG. 5 is a timing chart showing signal timings during data transfer of a general Centronics interface.

FIG. 6 is a flowchart showing an example of the overall processing procedure of an embodiment of the present invention.

7 is a flowchart showing an example of processing executed by a host computer in the communication control timing adjustment processing of FIG.

8 is a flowchart showing an example of processing performed by a printer in the communication control timing adjustment processing of FIG.

FIG. 9 is a timing chart showing signal timings during data transfer of the Centronics interface in another embodiment of the present invention.

FIG. 10 is a flowchart showing an example of processing performed by the printer in the communication control timing adjustment processing according to another embodiment of the present invention.

[Explanation of symbols]

 10 Host Computer 11 Centronics Interface 12 Printer Driver 13 Communication Control Timing Adjustment Flag 14 Response Waiting Maximum Time Register 20 Printer 21 Centronics Interface 22 Control Section 23 Command Analysis Section 24 Printer Engine 25 Expansion Memory 26 Communication Control Timing Adjustment Flag 27 Host Response Time Register 28 Timer section 29 Bus 30 Centronics interface cable

Claims (5)

[Claims] 1. An image forming system including a host device for outputting image information, a Centronics interface, and an image forming device connected to the host device via the Centronics interface, wherein communication control timing to the image forming device is provided. After issuing the command, the predetermined first data is transferred, and the image forming apparatus waits for the nACK signal pulse which is a response to the reception of the data for a predetermined time, and the nACK signal pulse cannot be detected within the predetermined time. In this case, the first data is again transferred to the image forming apparatus, these operations are repeated until the nACK signal pulse is detected, and when the nACK signal pulse is detected, the predetermined second data is transferred to the image forming apparatus. To the host device that ends the communication control timing adjustment process by transferring the communication control timing command to After the data received from a host device, until receiving the second data, the nA each receive a transfer of the first data
Delay the timing of outputting the CK signal pulse,
An image forming system, comprising: an image forming apparatus that uses a timing time when receiving the second data as a communication control timing when transferring image information data. 2. An image forming apparatus connected to a host device via a Centronics interface, and communication means for receiving a signal such as image information from the host device via the Centronics interface and transmitting a response signal, and the host device. A communication control timing adjustment command is issued by a flag setting means for setting a communication control timing adjustment flag indicating that the communication control timing of the Centronics interface is being adjusted, and the communication control timing adjustment flag is set. When the data is received from the host device, the timing of outputting the nACK signal pulse, which is a response signal, is changed so that the nACK signal pulse is output at the shortest timing that the host device can recognize. The communication control An image forming apparatus comprising: an output timing adjusting unit that adjusts the aiming; and a storage unit that stores the value of the communication control timing adjusted by the output timing adjusting unit. 3. The communication control timing of the communication means,
The image forming apparatus according to claim 2, wherein the image forming apparatus is variable according to a value of the communication control timing stored in the storage unit. 4. The host device has flag setting means for setting a communication control timing adjustment flag indicating that the communication control timing of the Centronics interface is being adjusted after the communication control timing adjustment command is issued, The image forming apparatus according to claim 2 or 3, wherein a signal indicating that the nACK signal pulse is detected is output to the image forming apparatus and the communication control timing adjustment flag is reset. 5. A data transfer control method for an image forming system, comprising: a host device that outputs image information; a Centronics interface; and an image forming device connected to the host device via the Centronics interface. A procedure for issuing a communication control timing command to the image forming apparatus, and the image forming apparatus that has received the communication control timing command from the host apparatus falling or rising of the nSTROBE signal is a response signal nACK.
A step of changing the timing of outputting the signal pulse by delaying each time from the shortest time for each data transfer, and a step of outputting a recognition signal indicating that the host device recognizes the nACK signal pulse when recognizing the nACK signal pulse, Data transfer control, wherein the image forming apparatus uses the shortest timing recognized by the host apparatus in response to the reception of the recognition signal as the output timing of the nACK signal pulse at the time of data transfer of the image signal. Method.