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VIPA System MICRO
8.2 Principle of the data transfer
RS485 PtP communication
1
Program
2
Protocol
3
FIFO buffer
4
Interface
HB400 | CPU | M13-CCF0000 | en | 18-50
The data transfer is handled during runtime by using FC/SFCs. The principle of data
transfer is the same for all protocols and is shortly illustrated in the following.
n
Data, which are written into the according data channel by the CPU, is stored in a
FIFO send buffer (first in first out) with a size of 2x1024byte and then put out via the
interface.
n
When the interface receives data, this is stored in a FIFO receive buffer with a size of
2x1024byte and can there be read by the CPU.
n
If the data is transferred via a protocol, the embedding of the data to the according
protocol happens automatically.
n
In opposite to ASCII and STX/ETX, the protocols 3964R, USS and Modbus require
the acknowledgement of the partner.
n
An additional call of the FC/SFC 217 SER_SND causes a return value in RetVal that
includes among others recent information about the acknowledgement of the partner.
n
Further on for USS and Modbus after a SER_SND the acknowledgement telegram
must be evaluated by a call of the FC/SFC 218 SER_RCV.
Option: PtP communication
Principle of the data transfer
203
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