Manual VIPA CPU 21x Chapter 9 Deployment CPU 21xSER-1
HB103E - Rev. 05/45 9-3
Protocols and procedures
The CPU 21xSER-1 supports the following protocols and procedures:
• ASCII communication
• STX/ETX
• 3964R
• USS
• Modbus
ASCII data communication is one of the simple forms of data exchange.
Incoming characters are transferred 1 to 1.
At ASCII, with every cycle the read-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 is to be found at ftp.vipa.de.
STX/ETX is a simple protocol with start and end ID, where STX stands for
Start of Text and ETX for End of Text.
The STX/ETX procedure is suitable for the transfer of ASCII characters. It
does not use block checks (BCC). Any data transferred from the periphery
must be preceded by an 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.
The user data which includes all the characters between Start and End are
transferred to the CPU when the End has been received.
When data is send from the CPU to a peripheral device, any user data is
handed to the SFC 217 (SER_SND) and is transferred with added Start-
and End-ID to the communication partner.
Message structure:
STX2
Z1 Z2 Zn ETX1 ETX2
ZVZ
STX1
You may define up to 2 start and end characters.
You may work with 1, 2 or no Start- and with 1, 2 or no End-ID. As Start-
res. End-ID all Hex values from 01h to 1Fh are permissible. Characters
above 1Fh are ignored. In the user data, characters below 20h are not
allowed and may cause errors. The number of Start- and End-IDs may be
different (1 Start, 2 End res. 2 Start, 1 End or other combinations). If no
End-ID is defined, all read characters are transferred to the PLC after a
parameterizable character delay time (Timeout).
Overview
ASCII
STX/ETX
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