981
Serial Communications Instructions Section 3-24
Holding the Receive Area 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.
0 1 0 0
0 2 0 0
R
3
2
Sent
Note
Protocol
Macro
Execution
Flag
Communica-
tions Port En-
abled Flag
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
R(1),2: 2 bytes sent
from D00101
Used as
send area
Received
W(1),2: 2 bytes received
starting from D00201
Received
data
As shown above, the symbol read option, R( ),
in the send message or the symbol write op-
tion
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