Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual User Manual
Page 162
Network and Application Layer Protocols
Chapter 12
12Ć15
In this format, A1 through A24 represents the 1 to 24 bits of the physical
address. For example, to address a command message to physical word
address 12,200 decimal (002FA8 hex) you would use the following binary
code in the address field:
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
1
0
1
0
0
0
0
0
1
0
1
1
1
1
First byte
Second byte
Third byte
Fourth byte
(value 00 hex)
(always 00 hex)
(value A8 hex)
(value 2F hex)
Packet Offset
A single message packet cannot transmit more than 244 bytes of user
data. To allow for data transfers of more than 244 bytes, the 1775–KA
module automatically transmits as many packets as necessary to complete
the message. Thus, a message may consist of several packets strung
together.
The packet offset is the difference (in 2 byte words) between the starting
address for the current packet and the starting address for the first packet
in the message. The packet offset for the first packet in the message is
always 0 (zero). Thus, adding the packet offset to the address field
specified in the message gives the destination address where the current
packet begins in the destination station.