Appendix
B
B1
Data Manipulation
This appendix describes how to address PLC-2 and PLC-3 programmable
controllers. It also describes the order of data transmission.
The memory address of an Allen-Bradley programmable controller may
take one of two forms—a logical address or a physical address.
Logical addressing refers to the type of addressing that a programmable
controller uses in its ladder-diagram program to access its own data table
memory.
Non-privileged commands access only the data table of programmable
controller memory. Because of the differences in programmable
controller memory organization, the logical addressing scheme varies with
the type of controller.
PLC-2 family controllers access their data tables by using an octal word
address. When you send a non-physical read or write command to a
PLC-2 family processor, however, you use a byte address to represent the
logical word address. To encode this logical byte address, double the
word address to get the corresponding byte address.
For example, to address PLC-2 Word 047, you would first convert the
Octal Value 047 to the desired base. Assuming that you are also using
octal, you then perform the next step. Doubling this value (047) gives
116
8
for the byte address.
What This Appendix Contains
Addressing PLC2 and PLC3
Controllers
Logical Addressing
PLC2 Logical Addressing