VIPA CP 240 RS232, Manual

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Chapter 4 CP 240 - serial Manual VIPA System 200V
4-10 HB97E - CP - Rev. 11/30
ASCII / STX/ETX / 3964(R) / RK512 - Basics
ASCII data communication is one of the simple forms of data exchange
that can be compared to a multicast/broadcast function.
Individual messages are separated by means of 2 windows in time. The
sending station has to transmit data messages within the character delay
time (ZVZ) or receive window that was defined in the receiving station.
The receiving station must acknowledge the receipt of the message within
the "time delay after command" (ZNA) or command window that was
defined in the sending station.
These time stamps can be used to establish a simple serial communication
link between PLC and PLC.
The Bit FRG is only reset when the data has been transferred and the ZNA
has expired.
Using ASCII a telegram is only handled over to the CPU when it has been
received completely. ASCII-fragmented allows you by means of the usage
of the Receive block FC11 (ASCII_FRAGMENT) to handle on big
telegrams to the CPU in blocks as soon as they have been received. For
this the block length is 12Byte. With ASCII-fragmented the CP doesn’t wait
until the telegram has been received completely.
STX/ETX is a simple protocol employing headers and trailers. The
STX/ETX procedure is suitable for the transfer of ASCII characters
(20h…7Fh). It does not use block checks (BCC). Any data transferred from
the periphery must be preceded by an STX (Start of Text) followed by the
data characters. An ETX (End of Text) must be inserted as the terminating
character.
The effective data, which includes all the characters between STX and
ETX, are transferred to the CPU when the ETX has been received.
When data is sent from the CPU to a peripheral device, any user data is
handed to the CP 240 where it is enclosed with an STX start character and
an ETX termination character and transferred to the communication
partner.
Message structure:
STX2 Z1 Z2 Zn ETX1 ETX2
ZVZ
STX1
You may define up to 2 start and end characters. It is also possible to
specify a ZNA for the sending station.
ASCII
ASCII-
fragmented
STX/ETX