Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual - Manual (Page 154)

Data Encoding and Addressing
Chapter 6
6-17
PLC-4 Microtrol
PLC-4 Microtrol controllers use physical addresses that begin at 00 for
the first word of memory and continue to 5FF hex for the last word of
memory. Figure 6.11 is a map of PLC-4 physical memory.
Figure 6.11
PLC-4 Physical Memory
Physical Byte
Address
(Hex)
Read Only
Read/Write
Force Table
I/O and Flags
Store Bits
Timers/Counters
Program Area
Sequencer Table
0
13
29
2A
31
32
7F
FF
100
5FF
11703
Specifying a physical address in PLC-4 privileged commands requires
3 bytes. The first byte is the identification number for a particular
controller in the loop, and it is labeled “PLC-4 SEL” in the command
message formats (Chapter 5). The next two bytes contain the physical
address of a word in the selected controller’s memory, and they are
labeled ADDR in the command message formats (Chapter5). When
encoding the physical address, be sure to put the low byte of the address
value in the first byte of the ADDR field.
Symbolic Addressing
Symbolic addressing uses ASCII symbols to represent a logical address.
Only PLC-3 controllers can accept symbolic addresses. Before using a
symbolic address in a message, you must first define the symbol at the
PLC-3 or PLC-5 that is to receive the message (refer to
Publication 1775-801).