10 TROUBLESHOOTING

10.1.3 Reading the RS-232 control signal status

MELSEC-Q

This section explains how to read the control signal status stored in the buffer memory during communication using RS-232 interface.

When GX Configurator-SC is used, check the status using the "Transmission control and others monitor/test" screen (see Section 8.6.3).

When a transmission problem occurs, read operation is executed to check the signal on/off status of the RS-232 interface.

(1) RS-232 control signal status storage area (address: 254H, 264H)

The status of the RS-232 signals is stored in buffer memory addresses 254H and

264H as follows:

b15

to

b6 b5

b4 b3

b2

b1

b0

Buffer memory address 254H

0

 

1/0

1/0

1/0

1/0

1/0

1/0 (Information on CH1 side)

 

 

 

 

 

 

 

 

 

 

 

264H

0

 

1/0

1/0

1/0

1/0

1/0

1/0 (Information on CH2 side)

 

 

 

 

 

 

 

 

 

 

 

1

: ON

RS

0

: OFF

DSR

 

 

 

 

DTR

 

 

CD

System area for QJ71C24 (-R2)

 

CS

 

 

RI

REMARK

(1)For more details on signals for RS-232, see Section 3.2.1.

(2)Signals output from the Q series C24 side (RTS and DTR) are controlled by the operating system (OS) of the Q series C24.

They cannot be directly controlled by the sequence program.

(3)There is a maximum delay of 100 ms in signal status stored in the buffer memory above.

(2)Example of a program that reads from RS-232 control signal status storage area

The following shows an example of a program that reads the RS-232 control signal status.

(input/output signals X/Y00 to X/Y1F of the Q series C24)

Example of FROM instruction

Read co

mmand

Reads the status of RS-232 control signal on

 

 

 

 

the CH1 side from address 254H.

 

 

Reads the status of RS-232 control signal on

 

 

the CH2 side from address 264H.

 

b15

to

b6 b5 b4

b3

b2

b1 b0

 

D0

 

 

 

0

0

0

1

1

1

DTR signal: ON, DSR signal: ON, RTS signal: ON

D1

 

 

0

0

1

1

1

0

CD signal: ON, DTR signal: ON, DSR signal: ON

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