Omron SYSMAC CJ - REFERENCE MANUAL 01-2008 Reference Manual page 1021

Serial Communications Instructions
Protocol
Macro
Execution
Flag
2 words
1 word
Holding the Receive Area
982
Communica-
tions Port En-
abled Flag
R
Unit address of communications partner
E1 hex: Inner Board
Serial port number (physical port)
2 hex: Port 2
Communications port number (logical port)
7 hex: Logical port 7
Communications sequence number
0065 hex: 101
3
R(1),2: 2 bytes sent
Used as
from D00101
send area
2
W(1),2: 2 bytes received
Received
starting from D00201
data
Note
The receive buffer is cleared to all zeros immediately before a communica-
tions sequence is executed for PMCR(260). If programming such as that
shown below is used to periodically read PV data or other values and data
cannot be read due to a reception error or other cause, the data being read
will be cleared until the next successful read.
A function is provided to maintain the data in the receive area even when a
reception error occurs. If this function is used, data will be transferred from the
first m words of the receive area to the receive buffer after the buffer is cleared
to all zeros but before the communications sequence is executed. This pre-
vents the receive area from being temporarily cleared to all zeros by writing
the most recent receive data when new receive data is not successfully
obtained.
Specify the number of words of the receive area to be maintained as the value
m. If 0 or 1 is specified, the holding function will be disabled and the receive
area will be cleared to all zeros.
Sent
0 1 0 0
Received
0 2 0 0
As shown above, the symbol read option, R( ),
in the send message or the symbol write op-
tion, W( ), actually sends/receives data.
Section 3-24