Siemens SIMATIC CP 340, User Manual

Page: 70 / 200

Basic Principles of Serial Data Transmission
2.7 Parameterization Data
PtP coupling and configuration of CP 340
70
Manual, 04/2011, A5E00369892-03
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 Description Range of values Default value
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).)
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.

Yes
 No
Yes
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).)
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.
1 to 250 250
Prevent overwriting 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.

Yes
 No (only if "Buffered
received message
frames" = "1")
Yes
For more information, refer to the Chapter "Receive Buffer on CP 340 (Page 55) ".