IDENT-I • IRI-KHD2-4.RX, IRI-KHA6-4.RX
Operating control interface units using the 3964R protocol
Subject to reasonable modifications due to technical advances.
Copyright Fuchs, Printed in Germany
Fuchs Group • Tel.: Germany (06 21) 7 76-0 • USA (330) 4 25 35 55 • Singapore 7 79 90 91 • Internet http://www.pepperl-fuchs.com
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8.1.1
Byte description:
1
Message identification, 00h, or FFh for any follow-up message
2
Message identification, always 00h
3
SEND (’A’) or FETCH (’E’) command. Byte 3 is an ASCII character
4
Command type, .i.e. type of data to be transmitted
5 and 6
Target address for SEND, or source address for FETCH
Byte 5 = DB number, Byte 6 = DW number
7 and 8
Volume of user data to be transmitted, in bytes or words, depending
on data type
9
Byte number of the coordination marker, or FFh when no coordina-
tion marker is defined. In the case of control interface units, this byte
is always FFh.
10
Bits 0 to 3: Bit number of coordination marker. If no coordination
marker is defined, this byte is always Fh.
Bits 4 to 7: CPU number, expressed as a digit from 1 to 4. If no CPU
number is specified, but there is a coordination marker, it is taken as
0h. Where there is neither a CPU number nor a coordination marker,
it is Fh. In the case of control interface unit, this is always FFh.
The control interface unit do not use bytes 4 to 8. Their content is copied in the re-
sponse message.
8.1.2
Handshake procedure
To establish communication, the control system sends the ASCII control character
STX (Start of Text). The control interface unit responds with the ASCII character DLE
(Data Link Escape), after which the user information is transmitted. Whenever it ap-
pears in the user data, the character DLE is sent twice. When the data has been trans-
mitted, the control system inserts the characters DLE ETX BCC, indicating the end of
transmission, and waits for a DLE acknowledge character from the control interface
unit. The data is verified with the block check character, BCC. BCC is the longitudinal
even parity (EXOR logic operation on all data bytes) of the block transmitted or re-
ceived. The calculation begins with the first byte of user data after communication is
established and ends after the characters DLE ETX when communication is terminat-
ed.
The control system sends the control character STX to establish communication. If
the control interface unit responds with DLE before the time-out for acknowledgment,
the protocol switches to send mode. If the control interface unit responds with NAK or
any character other than DLE, or if the acknowledgment time delay elapses without a
response, communication fails. With Siemens control systems, the procedure is
abandoned after 6 unsuccessful attempts, and the error is registered in the coordina-
tion byte KBS.
’D’
=
Data block
Byte 4 is an ASCII character
