Mitsubishi FX3U-232-BD User Manual page 477

FX Series PLC User's Manual - Data Communication Edition
Non-Protocol Communication (RS/RS2 Instruction)
3. Operation of the time-out check flag (which is not provided in FX
(before Ver. 2.00) PLCs)
When data receiving is suspended, counting of the timeout time is started immediately. If the PLC does not
receive the next set of data within the time-out time setting set by D8129, the time-out check flag (M8129) is
set to ON. At this time, the receiving complete flag (M8123) is set to ON also.
The time-out time setting (D8129) can be set to a value from 1 to 255 (10 ms to 2550 ms).
Receiving
Data
Timeout determination
M8129
Receiving complete
M8123
The time-out check flag (M8129) does not turn OFF automatically.
Set it to OFF in the sequence program. (When M8123 is set to OFF, M8129 is also set to OFF.)
Using this function, the PLC can receive data from equipment where the amount of send data varies without
the terminator.
4. When the control line is set to interlink mode
When interlink mode is selected as the communication format, the following sequence is adopted from the
start of receiving to completion:
1) When the amount of data already received becomes "number of bytes to be received -30", the control line
ER (DTR) turns OFF.
When the control line ER (DTR) turns OFF, the external equipment should suspend data sending.
After the control line ER (DTR) turns OFF, the PLC can receive up to 30 characters (bytes).
2) When the external equipment suspends data sending, the PLC sets the time-out check flag (M8129) and
receiving complete flag (M8123) to ON after the time-out time setting (D8129).
Move the received data in a sequence program, and then set the receiving complete flag (M8123) and
time-out check flag (M8129) to OFF.
3) When the receiving complete flag (M8123) is set to OFF, the control line ER (DTR) turns ON.
When the control line ER (DTR) turns ON, resume sending data from the external equipment.
4) Repeat steps 1) to 3) until data receiving is completed.
5. Cautions on receiving
When receiving data, observe the following cautions:
1) While the receiving complete flag (M8123) is ON, the PLC cannot receive the next set of data.
When the receiving complete flat is set to OFF, the PLC waits to receive.
2) When RS instruction is driven, the receiving complete flag (M8123) remains OFF in an FX
FX PLC if the amount of received data (n) is "0", but the PLC does not wait to receive.
1NC
To make the PLC wait to receive, it is necessary to set the amount of received data "n" to "1" or more and
set the receiving complete flag to OFF from ON.
Receive data is suspended.
D8129 Set to OFF in sequence program.
× 10 ms
ON
ON
6 Creating Programs (RS Instruction)
6.2 How to Use RS Instruction
, FX (FX), FX , and FX
0N 2 2C
, FX
1S
A
2N
B
C
D
E
F
G
, or
1N
H
I
Apx.
F-39