Rockwell Automation 2755 Enhanced Decoder Series B - Manual (Page 267)

16–2 PCCC Host Commands
Publication 2755-833
!
ATTENTION: When controlling discrete outputs
locally using AUX port configuration, suspend host
communications to prevent outputs from
unintentionally changing state.
Command Format
The general structure and definitions of all commands is shown
below. The structure shows the high and low byte of each data word
(word
= 2 bytes). Data is always transmitted with the low byte of each
data word first and then the high byte. In the command explanations
below, MSB stands for Most Significant Bit, and LSB stands for
Least Significant Bit.
5
0 STS CMD
High Address FNC Code or Low Address
Transaction Number Sequence (TNS)
Data
122 or 124 bytes maximum
High Byte Low Byte
MSB LSB
1
3 2
4
6
.
.
.
126
7
.
.
.
127
•
CMD
Byte 0 specifies the command to perform.
Bits 0, 1, 2 and 3 of the CMD byte contain the command code.
The options are:
– 0001(01H) = Unprotected Read Command
– 1000 (08H) = Unprotected Write Command
– 0110 (06H) = Diagnostic Command
Bit 6 is cleared (0) for the command and set (1) for the reply.
Bit 4, 5, and 7 are always zero.
To send an unprotected write command, CMD byte 0 would look
like this:
LSB
0 0 0 0 1 0 0 0
7 6 5 4 3 2 1 0
1000 = Unprotected Write (08H)
Bit 6 cleared
(0) for com-
mand
Always 0
MSB