Omron CQM1H-SCB41 Operation Manual page 105

Using Protocol Macros
Transmission Reception buffer cleared
mode
Half-duplex Just before sequence execution
and at the end of SEND operation
for SEND or SEND&RECEIVE
commands
Note
90
Transmission Methods
Although the following two transmission methods are commonly used, only
half-duplex transmissions are supported for CQM1H protocol macros.
Half-duplex: Data can be sent only one direction at a time.
A
Full-duplex: Data can be sent in both directions at the same time.
A
The use of half-duplex transmissions presents some restrictions. Data
received from just before the SEND operation through the end of the SEND
operation cannot be received as receive data for the next RECEIVE operation
because the reception buffer is cleared just before a sequence is executed
and at the end of the SEND operation (i.e., for the SEND and
SEND&RECEIVE commands).
Between end of SEND operation and end
of RECEIVE operation or between the end
of SEND operation and just before begin-
ning of next SEND operation
An example timing chart for the above situation is shown below.
Sequence execution
Reception buffer cleared
Character trace
1. Data received before the completion of the SEND operation will be lost, but
it will be included in the character trace.
2. There is a time lag between the completion of data send processing and
the end of the SEND operation. This time lag is time t1 and is shown in the
following table. If the response from the external device is too quick, any
receive data entering between the end of sending data for the SEND oper-
ation and the completion of the SEND operation will not be received.
SEND operation
Data send processing
Quick response
Data reception
B A
Or
B
Data reception
Receive
Data received
See note 1.
t1
Time lag (See table.)
Reception buffer cleared
Section 5-7
B
Character trace
All characters while
tracing is being per-
formed
Send Receive
Data not received here