Omron CJ1W-SCU32 Operation Manual page 152

4 Using Protocol Macros
If a timeout occurs, a command end code (0204 hex (Remote node busy)) is returned to the com-
mand source. The send processing is not executed and the received command is discarded.
Protocol Macro Transmission Method
Set half-duplex (FALSE) or full-duplex (TRUE) depending on the transmission mode for the external
device.
Additional Information
Half-duplex: Allows data to be sent between two Units in only one direction at any one time.
Full-duplex: Allows data to be exchanged both ways between two Units at the same time.
With half-duplex transmissions, the reception buffer is cleared immediately before the sequence
is executed and immediately after Send completion (Send or Send&Recv command). Therefore,
the data received before and during Send execution cannot be received as receive data by the
next Recv command.
Precautions for Correct Use Precautions for Correct Use
When you use Send with half-duplex transmission, there is a time lag, t1, between data send
processing completion and Send completion. Therefore, if there is a rapid response from the
remote device and a response is returned for Send after data is sent (communications or other
command) and before Send is completed, the response during that time cannot be received by
using half-duplex transmissions. If this problem occurs, use the full-duplex transmissions.
Also, if the external device is connected by using 2-wire connections from an RS-422A/485 port
(Refer to 3-3-2 Recommended RS-422A/485 Wiring Examples), send and receive data cannot
both be on the same transmission line at the same time. This will create an additional lag time,
t2, or 150 µs. If responses are received quickly from the external device, i.e., faster than t1 +t2,
create a send delay at the external device or take other measures to allow for the lag times.
Send
operation
Data send
processing
Data
reception
Time Lag t1
Baud rate (bps)
1,200
2,400
4,800
9,600
19,200
38,400
57,600
115,200
230,400
4-16
A B
or
A
t1 t2 = 150 µs
Rapid
Time lags (see following table)
response
Reception buffer cleared
Time lag (µs)
1,116
578
288
144
73
36
24
12
6
CJ-series Serial Communications Units Operation Manual for NJ-series CPU Unit(W494)
A B
B
Data cannot be received
during this time.