Rockwell Automation 2755-DM9, -DM9E High Speed Decoder - Manual (Page 115)

Chapter 8
Host Commands Using the RS-485 Interface
8–3
COMMAND (Byte 0) - The first byte indicates one of the following
commands:
•
Unprotected Read
•
Diagnostic
•
Unprotected Write
The command byte has the following structure:
•
Bits 7, 5, and 4 are always zero.
•
Bit 6 is cleared (0) for command, set (1) for reply.
•
Bits 0, 1, 2, and 3 contain the command code:
0001 = Unprotected Read
0110 = Diagnostic
1000 = Unprotected Write
Example: To send an unprotected write command the following data would
be sent as byte 0:
0 0 0 0 1 0 0 0
MSB LSB
1000 =
Unprotected
Write Command
Bit #6 Cleared
For Command
Always Set to 0
STATUS (Byte 1)- The second byte of a command indicates the status code
of any command response:
•
Bits 0 through 3 are reserved for local status codes.
•
Bits 4 through 7 are for remote status codes.
Note: Since the decoder does not implement local status codes, bits 0
through 3 are always cleared (set at 0).