Siemens SIMATIC CP 340 User Manual page 70

Basic Principles of Serial Data Transmission
2.7 Parameterization Data
Receive buffer on CP
The table below describes the parameters for the CP receive buffer.
Table 2- 9 Receive buffer on CP (ASCII driver)
Parameter
Delete CP receive buffer on
startup
(Where the buffering of
multiple message frames is
concerned, CP 340 works in
accordance with the FIFO
principle when transferring
message frames to the CPU
(ring buffer).)
Buffered receive message
frames
(Where the buffering of
multiple message frames is
concerned, CP 340 works in
accordance with the FIFO
principle when transferring
message frames to the CPU
(ring buffer).)
Prevent overwriting
For more information, refer to the Chapter "Receive Buffer on CP 340 (Page 55) ".
70
Description
You can specify whether the CP receive
buffer should be deleted on startup or an
existing (old) message frame should be sent
to the CPU.
You can specify the number of received
message frames to be buffered in the CP
receive buffer. If you specify "1" here and
deactivate the following parameter "prevent
overwrite" and cyclically read the received
data from the user program, a current
message frame will always be sent to the
CPU.
You can deactivate this parameter if the
"buffered receive message frames" parameter
is set to "1". This authorizes the overwriting of
the buffered received message frame.
Range of values
Yes

No

1 to 250
Yes

No (only if "Buffered

received message
frames" = "1")
PtP coupling and configuration of CP 340
Manual, 04/2011, A5E00369892-03
Default value
Yes
250
Yes