Section 4: Software Commands
8197 Instruction Manual
Page 4-29
4.3
RS-485 COMMAND STRUCTURE
The commands described here must conform to a specific command protocol.
The protocol is shown in Table 4-3:
FIELD SIZE DESCRIPTION
Start Word
2 Bytes
Unique characters <#> <$> used to
synchronize with data stream
Source Address
1 Byte
0-31= unit address
32-254= reserved
255= broadcast
Destination
Address
1 Byte
0-31= unit address
32-254=reserved
255= broadcast
Message Length 2 Bytes
Variable length from 1 to 502 bytes
Message
1 to 502 Bytes 4 character commands plus parameters
Check Word
2 Bytes
Running sum including all bytes after the
start word through the last message byte.
Stop Word
2 Bytes
Unique characters (<cr><lf>) used to
synchronize with data stream
TABLE 4-3 RS-485 COMMAND PROTOCOL
All inputs via the RS-485 port must follow this format, or they will be ignored.
The descriptions that follow are for the Message field of the commands. When
the first character of a command is ‘w’, this indicates the controller is writing
information to the 8197. If the first character is ‘r’, the controller is reading
information. The RS-485 Com port operates at 9600 baud. Character structure
is 1 start, 8 data, 1 stop, and no parity.
