VIPA CPU 21 Series, Manual

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Chapter 9 Deployment CPU 21xSER-1 Manual VIPA CPU 21x
9-8 HB103E - Rev. 05/45
Principles of data transfer
The data transfer is handled during runtime by using SFCs. The principles
of data transfer are the same for all protocols and is shortly illustrated in
the following.
Data that is into the according data channel by the PLC, is stored in a FIFO
send buffer (
f irst i n f irst o ut) with a size of 2x256Byte and then put out via
the interface.
When the interface receives data, this is stored in a FIFO receive buffer
with a size of 2x256Byte and can there be read by the PLC.
If the data is transferred via a protocol, the adaption of the data to the
according protocol happens automatically.
In opposite to ASCII and STX/ETX, the protocols 3964R, USS and Modbus
master require the acknowledgement of the partner.
An additional call of the SFC 217 SER_SND causes a return value in
RetVal that includes among others recent information about the
acknowledgement of the partner.
Further on for USS and Modbus master after a SER_SND the
acknowledgement telegram must be evaluated by call of the SFC 218
SER_RCV.
Protocol FIFO buffer
256Byte
256Byte
256Byte
256Byte
IN
OUT
RS232C/RS485
Interface Program
SER_RCV
SFC 218
CFG
RECEIVE
SEND
SER_SND
SFC 217
SER_CFG
SFC 216
CPU 21xSER-1
Overview
Principle