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Appendix A: RS-232 Control
For RS-232 communication, the port settings should be as follows:
General
Baud Rate
Start Bits
Data Bits
Parity
Stop Bits
The message format is as follows:
Start Byte
Destination ID
Command
End Byte
Data Checksum
All messages sent to the rack will receive a response. A typical command transaction is shown below.
The ACK/NAK field conveys information concerning the delivery of messages. The results of command operations are
contained in the data field of an ACK message. NAK reason bytes are defined below.
Manual 19854 Rev. D
ECN 50523
RS-232, DCE interface, XON/XOFF flow control,
Asynchronous protocol
9600 Baud
1
8
None
1
Start
Destination
Byte
ID
(0x02)
(Rack/Slot)
STX (0x02) - marks the start of a new message.
16 bits - rack code (0-3 ASCII) followed by slot address (0-9 ASCII). Messages meant for
the master will have "MM" in this field.
Contains the command followed by any associated data. See below for command
structure, and command set for examples.
ETX (0x03) - marks the end of the message.
16 bits - the ASCII hex of the 8-bit sum, ignoring overflows, of all bytes in the message
including SOT and ETX bytes.
Host
Start
ACK
Byte
(0x06)
(0x02)
The Format of an ACK Message
Command
End
Byte
((0x03)
Rack
Command
ACK [data]
NACK [reason]
Data
End
Field
Byte
(0x03)
443B101/443B102
Checksum
Checksum
7
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