JP2000259559A - Serial interface circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce signal lines for an interface and to prevent transmission time from being prolonged when a plurality of serial devices having a three-wire type serial interface are loaded. SOLUTION: A controlled device selecting part 122 fetches a select signal sent via a signal line 110 with a clock and a strobe signal via signal lines 113 and 114 and outputs '1' to relevant selectors 123, 124.... Afterwards, when input data are outputted from a control part 101 via the signal line 110 and the clock is outputted via a signal line 111, respective devices 102, 103... to be controlled temporarily latch these input data, and the strobe signal via a signal line 112 passes only through the selector to which '1' is sent from the controlled device selector so that only the relevant device to be controlled can fetch the input data. At the time of outputting data from the device to be controlled, corresponding to the signal from the controlled device selecting part 122, a data output device selecting part 121 selects relevant data and outputs them to a signal line 115.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a serial interface circuit, and more particularly to a serial interface circuit suitable for a digital circuit on which a device having a plurality of three-wire serial interfaces is mounted.

[0002]

2. Description of the Related Art ROM, RAM, D / A converter, A
One of the data input methods of the / D converter and the like is a three-wire serial interface. FIG. 3 is an explanatory view showing the serial data input line 302 for input data DI to the device 301, a data shift clock line 303 for a clock SK for taking in the input data, and a load for a load signal LD for determining shift data. A line 304 is provided. The input data DI is sequentially taken into the shift register in the device one bit at a time by the clock SK, and when the load signal LD is given to the device (when the device is selected), the input data is determined and the device 30
1 is processed internally. If there is output data DO, it is output from the output line 305. Hereinafter, the load signal is referred to as a strobe signal (STB).

In a digital circuit equipped with a plurality of devices having such a three-wire serial interface, as shown in FIG. 4, in order to control input to each of the devices 402 to 404, a control unit 401 Three signal lines (for data, clock, and strobe) are arranged for each device. Also, in the case of a device having no input data and operating as an output device, as shown in FIG.
A clock line for data shift for shifting O and serial output, a load line for determining the shift data, and an output line will be provided. In the case of ROM, RAM, etc., an address line is also required. is there.

Some serial devices are of a three-wire type like FIG. 3, but output the most significant bit of an internal register for setting input data DI to an output line DO. In this case, to connect the control unit 601 and the devices 602 to 605 as shown in FIG.
The devices 602 to 604 are sequentially used as shift registers, and data is input by supplying a strobe signal when data has just entered the device 605 via these devices.

[0005]

When a three-wire or four-wire interface is configured with each device as shown in FIG. 4 or 5, when the number of devices is n, the number of signal lines or control lines is 3n or 4n lines are required, which complicates the wiring of the digital circuit and increases the number of steps. Also, if the device is cascaded as shown in FIG.
Although the number of signal lines can be reduced, there is a problem that data input takes time depending on a device. In the case of this cascade connection, if the timing of the shift clock and the strobe signal do not match, a malfunction may occur in many devices.

An object of the present invention is to provide a serial interface circuit capable of controlling many serial devices without increasing the number of signal lines and without causing an increase in data transmission time or a malfunction. It is in.

[0007]

According to the present invention, there is provided a controlled device selecting means for selecting one controlled device in accordance with an input device selection signal, and a controlled device selected by this means. Gate means for outputting a data strobe signal input only to the first device, and a first signal line for serially transmitting the device selection signal to the controlled device selecting means and serially transmitting input data to the controlled device. A second signal line for transmitting a select shift clock to the controlled device selecting means; a third signal line for transmitting a selecting strobe signal to the controlled device selecting means; A fourth signal line for transmitting a data shift clock to each of the control devices; and a data strobe signal to each of the gate means. A fifth signal line for transmitting the controlled device selection signal to the controlled device selection means via the first signal line, and the selection shift clock via the second signal line at the same time. Is transmitted to the controlled device selecting means, and then the selected strobe signal is transmitted to the controlled device selecting means via the third signal line. First control means for controlling to set a signal, and after the controlled device selection signal is set to the controlled device selection means by this means, input via the first signal line At the same time as transmitting the data, the data shift clock is transmitted via the fourth signal line, and thereafter, the data shift clock is transmitted via the fifth signal line. Second control means for controlling the input data to be set in the controlled device selected by the controlled device selecting means by sending a control signal to each of the gate means. A serial interface circuit is disclosed.

Further, according to the present invention, a controlled device selecting means for selecting one controlled device in accordance with an input device selection signal, and reading out only output data from the controlled device selected by this means. Data output device selecting means for outputting as data, a first signal line for serially transmitting the device selection signal to the controlled device selecting means, and transmitting a selection shift clock to the controlled device selecting means And a third signal line for transmitting a selection strobe signal to the controlled device selecting means, and the controlled device selection signal via the first signal line. Sending the selection shift clock via the second signal line to the controlled device selecting means at the same time as sending it to the controlled device selecting means. And then sends the selection strobe signal to the controlled device selection means via the third signal line to control the controlled device selection means to set the controlled device selection signal. Control means for reading the read data output from the data output device selecting means after the controlled device selection signal is set to the controlled device selecting means by this means.
And a fourth signal line for transmitting read data from the data output device selection means to the control means.

[0009]

Embodiments of the present invention will be described below in detail. FIG. 1 shows a configuration example of a serial interface according to the present invention.
03, a signal line 110 through which data S_DAT flows to determine a controlled device or to control the controlled device, and a data shift clock D_CLK to control the controlled device.
Line 111 through which strobe signal D_STB determines shift of data for controlling controlled device
, A signal line 113 through which a data shift clock A_CLK for controlling the controlled device selection unit flows, and a control through which a strobe signal A_STB for determining the data shift for controlling the controlled device selection unit flows. Line 114, data R_ from the controlled device
A signal line 115 for transmitting DAT to the control unit 101 is provided. The control unit 101 is a sequencer, a state machine, or another logic circuit including a microcomputer or a logic gate.
Control.

The controlled device 120 includes the controlled device 10
., A microcomputer, a logic gate, a switch, or the like, and which of the controlled devices 102, 103,.
Controlled device selection unit 122, which is determined in accordance with signals 0, 113, and 114, includes a microcomputer, a logic gate or a switch, and outputs output data from the device determined by controlled device selection unit 122 to control line 115. A data output device selection unit 121 to be extracted;
And a logic gate or a switch. The selector is provided for each of the controlled devices 102, 103,... And supplies a strobe signal of the control line 112 to the controlled device determined by the controlled device selection unit 122. Are provided.

FIG. 2 is a block diagram showing a configuration example of the controlled device selecting section 122 and the selectors 123, 124.
The controlled device selection unit 122 includes a D flip-flop 2
The shift registers are composed of eight shift registers 01 to 208 in tandem, and D flip-flops 211 to 218 for taking out their Q outputs.
Each of 126 is an AND gate. In this configuration example, one of the inputs of the four serial devices and one of the outputs of the four serial devices can be selected. With this configuration, when the input 8-bit serial data S_DAT is set in the D flip-flops 201 to 208 by the shift clock A_CLK, the 8-bit data is taken into the D flip-flops 211 to 218 by the strobe signal A_STB. It is. Here, in the input data S_DAT, only one of the eight bits is “1”.
Assuming that the other data is "0", if the "1" is, for example, the D flip-flop 211, only the output of the selector 123 is output as "1" when the strobe signal D_STB becomes "1". The controlled device 102 is selected. When one of the D flip-flops 215 to 218 is “1”, the output data is extracted as data R_DAT_L from the data output device selection unit 121 or the corresponding device.

FIG. 7 is a timing chart showing the operation of the interface circuit shown in FIGS. Control unit 1
In step S01, a selection signal A_DAT for determining a device to be controlled is transmitted to the control line 110 as data S_DAT in FIGS. As a result, the selection signal A_DAT is written to the D flip-flops 201 to 208 forming the shift register of FIG.
Next, when the control unit 101 sends the strobe signal A_STB to the signal line 114, the D flip-flops 201 to 2
08 are set to the D flip-flops 211 to 218, respectively, so that only one of the D flip-flops 211 to 218 is set to "1" and the others are set to "0" as described above. .

When inputting data to the controlled device,
Following the above-described controlled device selection operation, the control unit 101
Transmits the input data D_DAT to the signal line 110 as data S_DAT, and simultaneously transmits the shift clock D_CLK to the signal line 111 in synchronization with the input data D_DAT. As a result, the input data D_DAT is set in the shift registers inside the controlled devices 102, 103,. After this setting is completed, the control unit 101 sets the strobe signal D_S
TB_1 is used as the strobe signal D_STB on the signal line 11
2, since “1” is input from the selecting unit 122 only to the selector corresponding to the selected controlled device, the strobe signal D_STB is supplied to this controlled device.
— 1 is input, whereby the input data is actually taken into the device. However, this operation is a case where the controlled device is of a type in which input data is once set in a shift register and is taken in by a subsequent strobe signal. However, some devices are called chip strobes. In this case, when the strobe signal is at a low level during input of the input data D_DAT, the data is captured. In the case of this type of device, the control unit 101 controls the strobe signal D in FIG.
_STB_2 is output.

When data is read from the controlled device, only one of the outputs from the controlled device selection unit 122 to the data output device selection unit 121 (the outputs of the D flip-flops 215 to 218 in FIG. 2) is " 1 ", the data output device selection unit 121 selects the output of the corresponding device based on this information, and
5 as read data R_DAT.

According to the above configuration, if there are six signal lines for input and output, an input / output interface can be realized irrespective of the number of controlled devices, and the number of control lines can be greatly reduced. The time for input / output does not increase significantly. In particular, in the case of a digital circuit having no output, it is sufficient to provide five control lines. In the above description, the controlled device selection unit 122 is a serial / parallel conversion circuit as shown in FIG. 2, but this may be a decoder type or another circuit, and the format of each signal or the like may be adjusted according to the circuit. Just choose the timing.

[0016]

According to the present invention, when n devices using the three-wire serial interface are controlled at a time and only one device is controlled at a time, five control lines and one data output from the controlled device are used. By using this, it is possible to provide a 6-wire serial interface capable of reducing the transmission time as compared with the cascade connection. Further, since the number of clocks for data transmission is reduced as compared with the case of the cascade connection, malfunctions can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of an interface circuit according to the present invention.

FIG. 2 is a block diagram illustrating a configuration example of a controlled device selection unit.

FIG. 3 is an explanatory diagram of a three-wire serial interface device.

FIG. 4 is an explanatory diagram of an input interface when a plurality of 3-wire serial interface devices are mounted.

FIG. 5 is an explanatory diagram of an output interface when a plurality of 3-wire serial interface devices are mounted.

FIG. 6 is an explanatory diagram of an input interface by tandem connection of a three-wire serial interface device.

FIG. 7 is a time chart illustrating an operation of the interface circuit of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Control part 102,103 Controlled device 110-115 Signal line 121 Data output device selection part 122 Controlled device selection part 123,124 Selector

Claims (2)

[Claims] 1. An apparatus according to claim 1, further comprising:
Controlled device selecting means for selecting one controlled device; gate means for outputting a data strobe signal input only to the controlled device selected by this means; and A first signal line for serially transmitting a device selection signal and serially transmitting input data to the controlled device; and a second signal line for transmitting a selection shift clock to the controlled device selecting means. A third signal line for transmitting a selection strobe signal to the controlled device selecting means; a fourth signal line for transmitting a data shift clock to each of the controlled devices; A fifth signal line for transmitting a data strobe signal to each of the means; and the controlled device via the first signal line. The selection shift clock is transmitted to the controlled device selecting means via the second signal line at the same time as transmitting the selection signal to the controlled device selecting means, and then the selecting signal is transmitted via the third signal line. Control means for controlling the controlled device selection means to set the controlled device selection signal by transmitting a control strobe signal to the controlled device selection means; and After the device selection signal is set to the controlled device selection means, the input data is sent out via the first signal line and
The data shift clock is transmitted through the signal line of the above, and then the data strobe signal is transmitted to each of the gate means through the fifth signal line, whereby the controlled device selecting means selects the data strobe signal. A second control means for controlling the input data to be set in the controlled device. 2. An apparatus according to claim 1, wherein said signal is one of:
Controlled device selecting means for selecting one controlled device; data output device selecting means for outputting only output data from the controlled device selected by the means as read data; and selecting the controlled device. A first signal line for serially transmitting the device selection signal to the unit; a second signal line for transmitting a selection shift clock to the controlled device selection unit; and a selection to the controlled device selection unit. A third signal line for transmitting a strobe signal for use, and the controlled device selection signal is transmitted to the controlled device selection means via the first signal line, and simultaneously via the second signal line. Sending the selection shift clock to the controlled device selection means; and then transmitting the selection straw through the third signal line. First control means for controlling the controllable device selection means to set the controllable device selection signal by transmitting a signal to the controllable device selection means; and Second control means for reading the read data output from the data output device selecting means after a signal is set to the controlled device selecting means; and reading from the data output device selecting means to this means. A fourth signal line for transmitting data; and a serial interface circuit.