JPS6034861B2 - Serial data transfer circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a serial data transfer circuit between devices, and more particularly to a serial data transfer circuit that uses a serial data line to monitor the connection state with a partner device.

The purpose of the present invention is to:
It is an object of the present invention to provide a novel serial data transfer circuit that can reduce the number of signal cables and easily and accurately monitor the connection state with a partner device located at a remote location.

According to the present invention, the transmitter/receiver circuit is configured of a transmitter/receiver circuit connected to a serial data transfer path consisting of a pair of transmission paths, and a switch for disconnecting only the transmitter circuit from the serial data transfer path. A serial IJ data transfer circuit is provided which is characterized in that it detects a connection state with a partner device by monitoring the voltage value of a received signal.

Next, a preferred embodiment of the present invention will be explained in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a serial data transfer circuit according to the present invention.

In FIG. 1, a serial data transfer circuit 1 and a serial data transfer circuit 2 are connected by a coaxial cable 3.

In the serial data transfer circuit 1, the transmitting circuit is composed of transistors Q, , Q2, and resistors R, to R4, and constitutes a non-saturated switching circuit.

The receiving circuit is composed of a comparison circuit Z, and its comparison voltage VR6
F is a voltage obtained by dividing the power supply voltage Vcc by resistors R6 and R7. When the receiving end voltage VRcv is higher than the comparison voltage VREF, the receiving output R becomes "H", and when it is lower, it becomes "L". RL indicates a relay, and the operation of the relay RL causes the serial data transfer circuit 1 to The transmitting circuit can be connected or disconnected from the coaxial cable.

On the other hand, the transmitting circuit and receiving circuit of the serial data transfer circuit 2 have the same configuration as that of the serial data transfer circuit 1, except that the relay circuit is not included. Identical parts of the transmitting and receiving circuits of circuit 2 are shown with the same reference symbols as in serial data transfer circuit 1, and a prime has been added. Setting of circuit constants and circuit operation will be explained below.

The resistor K3 of the transmitting circuit is set to the same low resistance value as the characteristic impedance of the coaxial cable to achieve impedance matching.

The transmission input terminal S is a TTL level transmission serial data input terminal, and is turned on and off (i.e. “L”, “
otherwise, it is clamped to "H".

The transistor Q2 is conductive only when the transmission input terminal S is "L", and the collector current lc at that time is the resistor R,,R2
, R4.

At this time, the transistor Q2 is activated in a linear operation region where oversaturation does not occur. Therefore, the collector current lc of transistor Q2 has a constant value when it is conductive. In the case of normal serial data transfer, the relay RL energizes the magnet with the relay magnet drive signal RL, and keeps the relay RL closed.

At this time, the receiver voltage VR of serial data transfer circuits 1 and 2
cv and VRcv' are given by the following equations. Equation (1} becomes Equation (2) when transistors Q2 and Q2' are cut off.
is the case when transistors Q2 and E2' are suitable conductors. VMv (''H'') = VMv'gH') Main VM
…'1}VRCvgL”)=VRcv′(''L”)
±VCC-R31C/2>○”.(2} However, R5=(
=R5')》》》R3=(R3') Therefore, the comparison voltage VREF' at the receiving end is VCC-R3/2<VRE
Resistor R6 so that F'<VCC ---[3}
', R7' may be used to set the comparison voltage VR town'.

Next, a method of detecting whether or not the connection with the other party's device via the coaxial cable is normal will be explained.

When transistors Q2 and Q2' are both "off", relay RL. The connection status can be detected by opening and closing. First, when the coaxial cable is connected to the other device and the power is turned on, the receiving end voltage switch of the serial data transfer circuit 1 is VRcv2Vcc regardless of whether the relay RL is open or closed.

That is, when the relay RL is closed, the ten inputs of the comparator circuit B are connected to the resistor R.
3. Connected to power supply voltage Vcc through a parallel circuit of relay contact rl, coaxial cable 3, and resistor R3', and relay R
At L, the tenth input of the comparator circuit B is connected to the power supply voltage Vcc through the coaxial cable 3 and the resistor R3', but as mentioned above, both transistors Q2 and Q2' are "off", so in either case , receiving end voltage VRcv VC
It becomes C. Second, when the coaxial cable is not connected to the other device, when the relay RL is closed, the ten inputs of the comparison circuit B are connected to the relay contact rl, and the power supply voltage Vcc is passed through the resistor R3.
When the relay RL is open, the ten inputs of the comparison circuit Z are grounded through the resistor 5, so the receiving end voltage VRcv becomes 0.

Third, the coaxial cable is connected to the other device,
When the power is not turned on, the ten inputs of the comparator circuit Z and the relay RL are grounded through the resistor R5, the receiving end voltage VRcv=0, the relay RL is closed, and the resistor R3 and (R3
'Internal resistance RP at power off)
vCC'Kanaru. The lower this voltage is, the more it can be distinguished from unconnected. Therefore, the lower the internal resistance RP when the power is turned off, the better. This can be easily achieved by adding a bleeder resistor having a lower resistance than the resistor R3 to the power output terminal. FIG. 2 shows a list of signal levels during each operation.

In FIG. 2, ■ indicates the fluctuation range of the receiver voltages VRcv, VRcv' when normally connected with the relay RL closed, and varies from the sardine voltage (vCC) to VCC-¥.

(3) corresponds to the second case, and when the coaxial cable 3 is not connected, the receiving end voltage VRcv becomes 10 Vcc when the relay RL is closed, and 0 when the relay RL is open. It is shown that. 3 corresponds to the third case, and indicates the fluctuation range of the receiving end voltage VRcv when the coaxial cable 3 is connected and the power of the serial data transfer circuit 2 is not turned on. It shows that when it is closed, it becomes rough XVCC, and when it is open, it becomes o. Here, RP indicates the internal resistance of the power supply when the power is not turned on. ■
corresponds to the first case, and when the connection is normal, the relays RL,
This indicates that the receiving end voltage VRcv is Vcc regardless of whether the terminal is open or closed. As is clear from FIG. 2, if the receiving end comparison voltages VREF and VREF' are set to satisfy the following equation, it is possible to discriminate between serial data "1" and "0" and to discriminate the connection state.

Taisancho XV ratio < V thin F < VM ...■ and VCC-R book C < VR8F < VCC ---'31
When the receiving end comparison voltage VREF is set to satisfy the '3l formula and the '41 formula, the connection state with the other party's device can be detected by the following procedure.

First, input terminals S and S' are set to "H", and relay R
If the reception output R is "L" when L is closed, it means that the power of the other party's device is not turned on.

Next, when relay RL is opened, if the reception output R is "L", the coaxial cable is not connected, and if it is "H", the coaxial cable is connected normally, and the power of the other device is also turned on. It can be detected that As explained above, the present invention uses a pair of data transmission paths and is configured to be able to transfer serial data and detect the connection state with the other party's device. It has the effect of significantly reducing Although the present invention has been described above with respect to one preferred embodiment thereof, this is merely an illustrative example, and it goes without saying that the present invention is not limited only to the embodiment described here.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a serial data transfer circuit according to the present invention, and FIG. 2 is a list of signal levels during each operation to explain FIG. 1. 1, 2... Serial data transfer circuit, 3...
・Coaxial cable, R, ~R7, R,'~R7'...
Resistor, Q,,Q2,Q,',Q2'...transistor,
Z,,Z'...comparison circuit, RL. ······relay,
rl. ...Relay RL contact. Figure 1 Tsutomu Figure 2

Claims (1)

[Claims] 1. A first transmitting/receiving circuit connected to one end of a serial data transfer path composed of a pair of transmission paths, a second transmitting/receiving circuit connected to the other end of the transfer path, and and a switch for disconnecting only the transmitting circuit of the first transmitting/receiving circuit, and detecting the connection state with the second transmitting/receiving circuit by monitoring the voltage value of the received signal when the switch is opened or closed. Characteristic serial data transfer circuit.