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VIPA System SLIO
6.6 Communication
6.6.1 FC/SFC 217 - SER_SND - Send to PtP
6.6.2 FC/SFC 218 - SER_RCV - Receive from PtP
6.7 Protocols and procedures
Overview
ASCII
STX/ETX
HB300 | CPU | 013-CCF0R00 | en | 16-40
This block sends data via the serial interface. The repeated call of the FC/SFC 217
SER_SND delivers a return value for 3964R, USS and Modbus via RETVAL that con-
tains, among other things, recent information about the acknowledgement of the partner
station. The protocols USS and Modbus require to evaluate the receipt telegram by
calling the FC/SFC 218 SER_RCV after SER_SND.
This block receives data via the serial interface. Using the FC/SFC 218 SER_RCV after
SER_SND with the protocols USS and Modbus the acknowledgement telegram can be
read.
More information about the usage of these blocks may be found in the
manual "SPEED7 Operation List" from VIPA.
The CPU supports the following protocols and procedures:
n
ASCII communication
n
STX/ETX
n
3964R
n
USS
n
Modbus
ASCII data communication is one of the simple forms of data exchange. Incoming char-
acters are transferred 1 to 1. At ASCII, with every cycle the read FC/SFC is used to store
the data that is in the buffer at request time in a parameterized receive data block. If a
telegram is spread over various cycles, the data is overwritten. There is no reception
acknowledgement. The communication procedure has to be controlled by the concerning
user application. An according Receive_ASCII FB may be found within the VIPA library in
the service area of www.vipa.com.
STX/ETX is a simple protocol with start and end ID, where STX stands for Start of Text
and ETX for End of Text.
n
Any data transferred from the periphery must be preceded by a Start followed by the
data characters and the end character. Depending of the byte width the following
ASCII characters can be transferred: 5bit: not allowed: 6bit: 20...3Fh, 7bit: 20...7Fh,
8bit: 20...FFh.
n
The effective data, which includes all the characters between Start and End are trans-
ferred to the CPU when the End has been received.
n
When data is send from the CPU to a peripheral device, any user data is handed to
the FC/SFC 217 (SER_SND) and is transferred with added Start- and End-ID to the
communication partner.
n
You may work with 1, 2 or no Start- and with 1, 2 or no End-ID.
n
If no End-ID is defined, all read characters are transferred to the CPU after a parame-
terizable character delay time (Timeout).
Deployment PtP communication
Protocols and procedures
163
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