Siemens SIMATIC CP 440, Руководство пользователя

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Programming Example – Standard Blocks
9-10
Point-to-point connection CP 440 Installation and Parameter Assignment
A5E00057742-02
Description of FC 21 (SEND)
Before you continue, please refer to the description of FC21 in the “CP440 SEND
RECV” example in Section 9.6.1.
The procedure for processing a SEND job cyclically is as follows:
At each block call, SEND_440 is run through with SEND_REQ=0. If neither
SEND_DONE nor SEND_ERROR are present, the block is terminated.
If SEND_DONE is present, SEND_440 is run through again with SEND_REQ=1.
If SEND_ERROR is present, SEND_440 is run through with SEND_REQ=0 and
then with SEND_REQ=1.
To ensure that SEND_440 can be run through with SEND_REQ=1 in the very first
pass, the SEND_STARTUP_ENDED bit is also evaluated in the program section
“Check if SEND_DONE or SEND_ERROR or not first Cycle”. This bit is at 0 during
the first pass and is then fixed at 1.
9.6.3 “CP440 ASCII BCC” Program Example
This program example only makes sense for the ASCII driver.
This example is set up identically to the “CP440 SEND RECV” example but also
contains the following:
•
A block check sum is generated in the send section by calling FC 23 (GEN
BCC)
•
The block check sum is checked in the receive section with the call of FC 24
(CHK BCC)