Rockwell Automation 2755-DM9, -DM9E High Speed Decoder - Manual (Page 114)

Chapter 8
Host Commands Using the RS-485 Interface
8–2
You can use RS-485 PCCC to communicate with a host programmable
controller using a PCCC format. The following diagram illustrates a PCCC
command.
00000010 01000001
DATA MAXIMUM OF 122 BYTES
HI Byte LOW Byte
1 0
3
4 5
2
7 6
10010010 00110000
10001000 00000000
01110000 00000010
128
B
Y
T
E
S
M
A
X
The diagram illustrates both the high byte 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. The numbers on the diagram indicate the
order in which data bytes are transmitted.
PCCC Command Format
The Programmable Controller Communications Commands (PCCC) are sent
in packets of data having the following structure.
STATUS COMMAND
TRANSACTION WORD
HI-ADDRESS
LOW-ADDRESS or
FUNCTION CODE
DATA
HI Byte LOW Byte
128
B
Y
T
E
S
M
A
X
The LOW-byte is always sent out first and then the HI-byte. The following
are descriptions of each field of the command:
RS-485 PCCC Command
Protocol