JPH022281A - Communication control equipment - Google Patents

Abstract

PURPOSE:To attain the communication control of ready/busy system through a pair of signal lines by forming a current loop when a terminal equipment reaches the ready state, reading the state by a host computer and transferring the data to the terminal equipment through a pair of the current loop signal lines. CONSTITUTION:In the case of the ready state in a terminal equipment PT, the communication control circuit 11 outputs a ready signal to a terminal DTR. The ready signal is outputted to a photocoupler 8 via a driver 10 to turn on a photo transistor acting like a switch means. Thus, the loop is closed and a current flows to the current loop signal line Lo. In the host computer HS, the photocoupler 4 detects the closed current loop signal line Lo and a read back means recognizes the ready state of the terminal equipment via a receiver 6. When the host computer HS recognizes the ready state, a data is outputted from a terminal TxD and the data is transferred through the photocoupler 3 and the current loop signal line Lo.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a communication control device in a system that uses a current loop interface communication method. The present invention relates to a communication control device that includes a terminal device and controls data transfer using ready/busy signals output from the terminal device.

(Prior Art) FIG. 3 is a configuration block diagram showing an example of a conventional device. In the figure, HS is a host computer, and P′l is a terminal device such as a printer that is controlled by the host computer HS. ! Connect the data line 1 to the machine HS.
], are connected by status line L2.

There is a communication control circuit 11 in the host meter +g machine HS that monitors the ready/busy signal sent from the terminal device side via the status line 2 and sends data on the data line L1 when it is in the ready state. Also, within the terminal device PT, there is a communication m'Jtl which sends a signal indicating the status of the terminal device side (ready state or busy state) to the status line L2 and receives data sent via the data line L1. '
There is a J circuit 21.

(Problem to be Solved by the Invention) The conventional communication control device with such a configuration has a total of three hosts! Two pairs of signal lines are required between the machine H8 and the terminal device P'F: a status line L2 for notifying the status of the terminal device and a data line L1 for data transfer.

The present invention has been made in view of these circumstances, and its purpose is to realize a communication control device that can perform one-way ready/busy communication control of a current loop interface using a pair of signal lines. It is in.

(Means for resolving the 11 problems) FIG. 1 is a block diagram 1 showing the basic configuration of the present invention. In the figure, HS is a host computer, and PT is a terminal device connected to this host computer W fi 1-I S via a pair of current loop signal lines Lo. In the six terminal device PT', 21 is a switch means that connects the current loop signal line LO to form a loop when it is in the ready state rl, and opens the loop of the current loop signal line LO when it is busy. Host total Wfi
In H5, 11 reads out the signal state on the current loop signal lines l and 0 to read out the signal state on the terminal device M P 'I'
This is a read pack means for knowing the ready state/busy state of the device.

(Function) In the terminal device 2. When it becomes ready, the switch means is turned on, a current loop is formed, and the host computer reads this state and transfers the data to the terminal device using a pair of current loop signal lines.

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

FIG. 2 is a block diagram showing an embodiment of the present invention. In the figure, parts that are the same as those in Figure 1 are designated with the same reference numerals.6 Host Total! In i[IIs, 1 is a communication control circuit iM, which uses a communication LSI that is already commercially available, and which connects the terminal '
The data to be transferred to I″x +) is output and the terminal DC
A signal indicating the presence or absence of current flowing through the current loop signal line 1o is applied to D, and a readback means for knowing the ready state/busy state of the terminal device PT is configured inside.

2 is a driver, 3 and 4 are current loop signals P+i1
．． 0, the transfer data output from the communication control circuit 1 is sent out onto the current loop signal line [, 0 via the driver 2 and photocoupler 3.

5 is a constant current source that supplies a constant current of, for example, 20 mA to the current loop signal line LO, and 6 is a receiver that receives a signal indicating the ready state/busy state sent from the terminal equipment ff1JT via the photocoupler 4, and its output. The signal is applied to the terminal DCD of the communication control circuit 1.

Coupler 3.4 to photo 1 is composed of a combination of a light emitting diode and a phototransistor.
In the photocoupler 3 for transmitting transfer data, a phototransistor is inserted into the current loop signal line Lo, and
The photocoupler 4 that receives the ready signal/busy signal is
A light emitting diode is inserted into the current loop signal line Lo.

In the terminal device PT, 7 and 8 are both photocouplers, which are composed of a light emitting diode and a phototransistor, and the photocoupler 7 that receives the transferred data is inserted into the light emitting diode or the current loop signal line Lo. In the photocoupler 8 which outputs a ready signal/busy signal, a phototransistor is inserted into the current loop signal line Lo. This phototransistor is
It functions as the switch means 21 in FIG. 9 is a receiver, 10 is a driver, 11 receives the data transferred via the receiver 9 at a terminal RxD, and outputs the ready signal / via the terminal D'I'R and the driver 10.
4, which is a communication control circuit that outputs a busy signal, operates as follows. @end device P1'
is in a busy state, the communication control circuit 11 connects the terminal D i”
Outputs a busy signal to H.

This busy signal is output to the photocoupler 8 via the driver 10, and turns off the phototransistor functioning as a switching means. As a result, the loop of the current loop signal line LO becomes open, and no current flows.

In the host total 3fiH8, the photocoupler 4 detects the opening of the current loop signal line Lo, and learns via the receiver 6 whether the read pack means or the terminal device is busy. Total number of hosts: 35. N I(s
does not perform data transfer operations in this busy state.

When the terminal device enters a ready state, the communication control circuit 11 outputs a ready signal to the terminal D'I'R to turn on the phototransistor functioning as a switch means. As a result, the current loop signal line LO becomes in a closed loop state, and current flows through the current loop signal line LO.

In the host meter gRH8, the photocoupler 4 receives and detects the closing of the current loop signal line [,0, and the read pack means via the receiver 6 knows the ready state of the terminal device. When the host calculation fiH8 learns of this ready state, it outputs data from the terminal GoxD and performs a data transfer operation via the photocoupler 3 and the current loop signal line Lo.

In the above explanation, the host meter 1fiH3 is configured to know whether the terminal device p'r is in a busy state or a ready state based on whether current is flowing through the current loop signal line Lo. In order to know the ready state of the terminal device, data is sent from the host 1fiH3, and the reception data received via the photocoupler 4 at that time is sent.
Determine whether it matches the data, and if it matches,
It may be assumed that the terminal device P'1' is in a ready state.

(Effects of the Invention) - As explained in detail, according to the present invention, communication control equivalent to the ready/busy one-way system can be performed using a configuration in which a host computer and a terminal device are connected using a pair of signal lines. We can provide a communication control device that can do this.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the basic configuration of the present invention, Figure 2 is a block diagram showing the basic configuration of the present invention.
The figure is a block diagram showing an embodiment of the present invention, and FIG. 3 is a block diagram showing the structure of a conventional device. H3...Host total X machine PT...Terminal device Lo...Current loop r W line 11...Lead pack means 21...Switch means 3.4.7.8...Photocoupler 2. 10...Driver 6.9...Receiver graduate 1 Figure 2

Claims (1)

[Scope of Claims] Consisting of a host computer and a terminal device connected to the host computer via a pair of current loop signal lines, the current loop signal is sent to the terminal device when the terminal device is in a ready state. The lines are connected to form a loop, and a switch means is provided to open the loop of the current loop signal line when the line is busy, and the state of the signal on the current loop signal line is read into the host computer. A communication control device comprising readback means for knowing the ready state/busy state of the terminal device.