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MELSEC-
A
8 OTHER FUNCTIONS
8.9.2 Precautions for using RS-232-C control signal read/write function
The precautions for reading the control signal status and controlling the output are
given below.
(1) Controlling the RS (RTS) signal with RYn9
Designate the RS (RTS) signal status designation (
R2
101H) to "1".
When "0" is designated for the RS (RTS) signal status designation (
R2
101H),
the RS (RTS) signal will constantly remain ON even if RYn9 is turned ON and
OFF.
(Follows the buffer memory side settings.)
(2) Controlling the ER (DTR) signal with RYnA
Designate "0" or "2" for the flow control designation (
R2
100H).
When "1" is designated, the RYnA ON/OFF will be ignored.
(3) Setting the buffer memory
When controlling the RS-232-C signal, designate in the R2 buffer memory shown
below.
R2 buffer memory
address
Name Details
R2
100H
Flow control
designation
Designate whether to carry out flow control with the DTR/DSR control or
DC code control when exchanging data between the R2 and external
device.
0 : Do not carry out flow control.
1 : Carry out flow control with DTR/DSR control. (Default value)
2 : Carry out flow control with DC code control.
R2
101H
RS (RTS) signal
status designation
Designate whether to leave the RS signal status constantly ON or to
follow the RYn9 ON/OFF state.
When the RS signal follows the RYn9 ON/OFF state, the RS signal will be
output as follows.
RYn9 = ON
RS signal = ON, RYn9 = OFF RS signal = OFF
0 : Always ON (RYn9 ON/OFF is invalid)
1 : Follow RYn9 ON/OFF
POINT
When the above buffer memory setting values have been changed, initialize the R2
with the process given in section 8.6.