JPH0467221B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] When communicating with a 2-channel serial communication source that generates communication requests asynchronously to each other using a microprocessor unit MPU that has a serial communication function for only one channel (ch), One channel transmits the same data twice at different intervals from other channels, and the other channel transmits data once.
On the MPU side, when both data collide, the latter data is received preferentially, and the former data is received when there is no collision, thereby achieving efficient communication.

[Industrial Application Field] The present invention provides asynchronous communication using a 1ch serial communication function.
This paper relates to a serial communication method for microcomputers that allows efficient acquisition of 2ch data.

[Conventional technology]

As shown in Figure 7a, device C (e.g. microprocessor MPU) which has only one channel of serial communication function takes in data from device A (e.g. keyboard KB) and device B (e.g. A/D converter ADC). In systems where this is necessary, data collisions can be avoided using the following methods.

(1) The signal timing of devices A and B is determined based on the transmission request from device C.

(2) Device C sends a reception confirmation signal, and devices A and B
transmits data until device C receives the signal.

(3) As shown in FIG. 7b, the transmission timings of devices A and B are shifted so that they do not overlap.

[The problem that the invention attempts to solve]

Method (1) is inefficient because it is not clear whether there is data transmitted by device A.

Method (2) requires bidirectional lines and dedicated signal lines, and the communication protocol is complicated.

Method (3) requires a signal to control timing.

The present invention is based on a method of retransmitting data from devices A and B at different cycles, and attempts to receive data while avoiding collisions of asynchronous data.

[Means for solving problems]

FIG. 1 is a basic configuration diagram of the present invention. Since device C has only one serial input terminal Si, serial data from devices A and B are selected by a changeover switch SW. This switching control of the switch SW is performed by the output of the port _P1 of the device C in synchronization with the data collection timing from the device B (for example, AD start). Device A is set to retransmit the same data twice at a different cycle than device B.

[Effect]

Device A transmits data at a timing that device C cannot predict. In response, device B returns data at a timing that device C can predict. Therefore, as long as device A does not transmit data, data can be collected without any problem.

On the other hand, if device A sends data asynchronously, data may collide. However, if the data retransmission period T _A and the data transmission period T _B are made different as shown in FIG. 2, even if one of the two data transmissions collides, the remaining one will not.

Specifically, the data transmission period T _B is set to be longer than the data retransmission period T _A , and in particular, the data transmission interval T _AB is set to be longer than the data retransmission period T _BW.
By making it longer, data can be prevented from colliding twice in a row.

When device C receives the data transmission start signal, it sets flag F (F=1). When a request for intermediate data occurs or when the received data is abnormal, the flag is reset (F=0). and,
When F=0, even if a serial signal on the data side is input, it is ignored until the transmission start signal is received again. On the other hand, if the data transmission end signal is normally received with F=1, the data has been successfully received, so F=0 is set and preparations are made for the next reception.

〔Example〕

FIG. 3 is a configuration diagram showing an embodiment of the present invention, and C
is a performance evaluation device for automobile engines. This device C has a function of receiving calculation instructions from the keyboard A, converting analog input data, and outputting the converted data from the D/A converter. For example, by changing the dynamic range of the sensor output (analog input) from keyboard A or adding an offset,
It is possible to output simulated characteristics of the sensor when it deteriorates.

The data uses 9600BPS asynchronous serial communication method as an example, and one data is as shown in Figure 4 a.
It has a 10-bit configuration. Of these, 8 bits excluding the start bit and stop bit constitute 1 byte, resulting in a total of 20 bytes of data as shown in Figure b. As an example, it is assumed that calculation instruction code [4]...Linear calculation (ax+b) Parameter 1 [100] = a Parameter 2 [50] = b Parameter 3 [ ] = Empty data.

On the other hand, the data has a 10-bit structure as shown in FIG. 4c, and is transmitted from the MSB first.

FIG. 5 is a flowchart of the control software executed by the CPU of device C. During AD conversion, the CPU sets port _P1 to 1 and switches the switch SW to the data side. When the AD conversion is completed, P ₁ is set to 0 and the switch SW is switched to the data side. Step S1 is to determine the level of this port _P1 . If P ₁ =0, a data reception error (for example, a frame error) is detected in step S2. If there is no error, flag F is checked in step S3, and if F=0, it is checked in step S4 whether it is a transmission start signal. If yes (Y) then step
Set F=1 in S5. This is the timing shown in FIG. Step S6 is the initialization of data array n.

If the result is Y in step S3, it is determined whether the process is finished in step S7, and if the result is no (N), the data is taken into the memory Pn in step S8, and the data is read in the memory Pn in step S9.
Increment the value.

When the result is Y in step S7, the number m of data is initialized in step S11, and the data in memory Pn is transferred to memory Qm in step S12. This is repeated until m=17 (steps S13, S14), and finally F=0 in step S15. This corresponds to the timing shown in FIG. 2 when the data acquisition is normally completed.

On the other hand, if it is determined in step S1 that P ₁ =1, a data reception error is determined in step S21.
If N, data is converted (data is taken in) in step S22, the next ADch is set in step S23, and P ₁ is changed to 0 in step S24.

The main routine shown in FIG. 6 sets P ₁ =1. Step S31 is executed once every 200ms, for example.
Determine AD timing, if Y, step
Set F=0 in S32. This timing is shown in FIG. In the next step S33, P ₁ is set to 1, and in step S34, ADch is output.

The above-mentioned timing is not the only time when the flag F becomes 0 at a timing other than that shown in FIG.
If a reception error is detected in the data in step S2 of FIG. 5, F=0 in step S10. This is not illustrated in the example of FIG. In either case, when F=0, the process returns from step S3 N to step S4 N, so subsequent data will not be captured until the transmission start signal is detected again.

〔Effect of the invention〕

As described above, according to the present invention, a microcomputer having only one channel serial communication function can efficiently communicate with an asynchronous serial communication source. In addition, bidirectional lines and dedicated signal lines,
Alternatively, a timing control signal is not required, and the communication protocol does not become complicated.

[Brief explanation of drawings]

Fig. 1 is a basic configuration diagram of the present invention, Fig. 2 is an explanatory diagram of its operation, Fig. 3 is a configuration diagram of an embodiment of the invention, Fig. 4 is an explanatory diagram of the data format, and Fig. 5 is an explanatory diagram of the present invention. FIG. 6 is a flowchart of the control software, FIG. 6 is a flowchart of the main routine, and FIG. 7 is an explanatory diagram of a conventional serial communication system.

Claims (1)

[Claims] 1. A device A that can transmit data at any timing to a microcomputer C that only has a serial communication function for one channel, and a device B that can transmit data at a timing specified by the computer. In a system in which data is transmitted asynchronously via serial communication, device A transmits the same data twice with different transmission cycles from device B, device C receives the data with priority, and the data is sent at a timing that does not collide with the data. A serial communication method for microcomputers that is characterized by switching inputs to receive signals.