Rockwell Automation 2755 Enhanced Decoder Series B - Manual (Page 268)

16–3 PCCC Host Commands
Publication 2755-833
•
STS
Byte 1 specifies the command status which is always 0.
•
TNS
Bytes 2 and 3 contain a unique transaction number sequence that
links each command to a reply
.
The TNS is user defined.
•
FNC Code
When the CMD byte = 06H (diagnostic command), byte 4
specifies a diagnostic function. For example, FNC = 01 means
read diagnostic counters.
•
Low Address
When the CMD byte = 01H (unprotected read command) or 08H
(unprotected write command
)
byte 4 contains the low byte of a
two byte address.
The low address (byte 4) and high address (byte 5) map to a
specific area in decoder memory for a read or write operation.
•
High Address
When the CMD byte = 01H (unprotected read command) or 08H
(unprotected write command
)
byte 5 contains the high byte of a
two byte address.
The low address (byte 4) and high address (byte 5) map to a
specific area in decoder memory for a read or write operation.
•
Data
The data area is command dependent. The starting byte for the
data area is also command dependent.
Command Reply Format
The general format and definition of a command reply is:
0 STS CMD Reply
TNS
Data 124 bytes maximum
High Byte Low Byte
MSB LSB
1
3 2
4
.
.
.
126
5
.
.
.
127
Optional
•
CMD Reply
Byte 0 contains the response to a command. Bit 6 is set for the
reply and responses are: