JPH0779344B2 - Half-duplex communication channel driver control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a driver control method for a communication device used in a half-duplex communication path, and more particularly to a method for disabling a transmission driver.

[Conventional technology]

Since the transmission side and the reception side do not have separate lines, only one communication channel can transmit at the same time (hereinafter referred to as "half 2").
A communication device that uses a “duplex communication path” uses a transmission driver except when it is transmitting by itself in order to prevent multiple communication devices from attempting to electrically drive the half-duplex communication path at the same time. Must be disabled.

A general communication system using a half-duplex channel is shown in FIG. In the figure, 1-3 are communication devices, 4 are half-duplex communication paths, 11, 21, 31 are microprocessors, 12, 22, 32 are communication controllers, 13, 23, 33 are transmission drivers, 14, 24, 34 is a receiving receiver, and a1 to a3 are control signals.

As described above, in FIG. 3, when the communication device 1 is transmitting, the communication devices 2 and 3 must not drive the half-duplex communication path 4. That is, only the communication device 1 must enable the transmission driver 13 and the other must disable the transmission drivers 23 and 33.

Therefore, each communication device enables the transmission driver before starting the transmission and disables the transmission driver after the transmission is completed. Therefore, it is necessary to know the timing of disenabling the transmission driver. That is, as shown in FIG. 4, a waiting time T1 from writing the last data to the communication controller 12 of the communication device 1 to disenabling the transmission driver 13 is provided (see FIGS. 4 (a) and (b)). )), Communication device 1 transmits driver 13 at time T2 after sending the last data DE.
Must be disabled (see FIGS. 4 (d) and 4 (b)). In addition, the communication device 1 must disable the transmission driver 13 at time T3 before the transmission driver 23 of the communication device 2 is enabled (see FIG. 4 (c)).

Usually, a dedicated IC (LSI) is used for the communication controller, and the microprocessor can write transmission data in byte (8 bits) units or several bytes in a batch to the communication controller. Therefore, the microprocessor waits until the written data is converted into serial data and sent out on the communication path, confirms the completion of transmission, and then disables the transmission driver.

However, some inexpensive communication controllers cannot confirm the completion of transmission, and in the case where such a communication controller has to be used, the following method has been conventionally used.

A microprocessor loops in a program to count time.

A timer is provided as hardware separately from the communication controller to count time.

[Problems to be Solved by the Invention]

Although the above method does not increase the cost, the microprocessor cannot perform other processing while counting the time of completion of transmission, which is a great limitation on the software configuration.

In the above method, the microprocessor can perform other processing while the timer counts, so it is not a constraint on the software configuration, but the cost is increased.

Further, in both of the above methods, unlike the case where the communication controller itself detects the completion of transmission, a margin must be taken into consideration, so the time from the completion of transmission to the disabling of the transmission driver should be longer than the minimum required time. I have no choice. Therefore, a time loss is caused by that amount, which becomes a factor of reducing the throughput of the entire communication.

The present invention has been made in view of such a point, and an object thereof is to add a restriction to the software configuration even when a communication controller that cannot confirm the completion of transmission is used in a half-duplex communication path. Another object of the present invention is to provide a method of confirming the completion of transmission, which does not require the addition of a hardware timer and does not cause a time loss that reduces the throughput of a communication path.

[Means for Solving the Problems]

In order to achieve such an object, the half-duplex communication path driver control method according to the present invention detects the timing of disenabling the transmission driver after the completion of transmission from the return reception.

[Action]

In the half-duplex channel driver control method according to the present invention, the transmission driver is disabled when the reception data matches the last transmission data.

〔Example〕

In the case of the half-duplex communication path, since the transmission driver and the reception receiver are wired-OR on the communication path, the transmission data can be returned and received at the same time as the transmission, and the transmission data written in the communication controller can be returned. If received by reception, the transmission data means that transmission on the communication path is completed. In general, a communication controller that cannot confirm the completion of transmission can also confirm the presence or absence of received data. That is, it is possible to issue an interrupt request at the time of reception and read the presence / absence of received data by a program. Therefore, after writing the last data of the transmission message to the communication controller, the return reception may be monitored and the transmission driver may be disabled when the last transmission data is received. This is shown in FIGS. 1 and 2.

FIG. 1 is a flow chart showing a method of judging the completion of sending when no interrupt is used, and FIG. 2 is a flowchart showing a method of judging the completion of sending when using an interrupt.

In FIG. 1, after writing the last transmission data to the communication controller, the presence or absence of the reception data is tested (steps 51 and 52). If there is no received data, the standby state is entered, and if there is, the received data is read (step 53).
Next, it is determined whether or not it matches the last transmission data (step 54). If they match, it is determined that the transmission is completed, and the transmission driver is disabled (step 55). If they do not match, return to step 52,
Test again for the presence of received data.

The operation shown in FIG. 2 is almost the same as the operation shown in FIG. 1, except that interrupt processing is performed. That is, step 61 having the same contents as step 51 is a part of the transmission side routine, and the arrow IR
If the receive interrupt indicated by I occurs, steps 62-64
Performs the reception interrupt routine of. First, the received data is read (step 62), and it is determined whether the received data matches the last transmitted data (step 6).
3) If they match, it is determined that the transmission is completed, and the transmission driver is disabled (step 64).
If they do not match, the process returns to the transmitting side routine and returns as shown by the arrow IR2.

[Effects of the Invention] As described above, the half-duplex communication path driver control method according to the present invention forms a loop by a program by detecting the timing of disenabling the transmission driver after the completion of transmission from the return reception. Since there is no need to count the time with a hardware timer, and there is no need to have a hardware timer, even when using a communication controller that cannot confirm the transmission completion in the half-duplex communication path, the hardware configuration is There is an effect that it is possible to obtain a method of confirming transmission completion without adding a wear timer and without time loss that reduces the throughput of the communication path.

[Brief description of drawings]

FIG. 1 is a flow chart for explaining an embodiment of a half-duplex communication path driver control method according to the present invention, FIG. 2 is a flow chart for explaining the second embodiment, and FIG. FIG. 4 is a system diagram showing a communication system of a half-duplex communication path, and FIG. 4 is a time chart showing enable and disable timings. 1,2,3 ... communication equipment, 4 ... half duplex communication path, 11,21,31 ...
… Microprocessor, 12,22,32 …… Communication controller, 13,23,33 …… Transmitting driver, 14,24,34 …… Receiver receiver.

Claims (1)

[Claims] 1. In a half-duplex communication path driver control method for a communication device using a communication controller that cannot confirm completion of transmission onto a half-duplex communication path, a timing for disabling a transmission driver after completion of transmission is folded back. A half-duplex communication path driver control method characterized by detecting from reception.