Physical Addressing; Plc 2 Physical Addressing - Allen-Bradley 1779-KFMR User Manual

Appendix B

Physical Addressing

PLC 2 Physical Addressing

Physical addressing is the type of addressing a computer would use with
one of these physical commands:
Physical Read (PLC-2 and PLC-3 Controllers)
Physical Write (PLC-2 and PLC-3 Controllers)
Diagnostic Read
In particular, you would use physical addressing to upload or download
programmable controller memory.
Because of the differences in programmable controller memory
organization, the physical addressing scheme varies somewhat with
controller type.
In the program area of memory, the physical address equals the logical
address. In the data table area of memory, to convert a given logical
address to its corresponding physical address, move Bit 7 of the logical
address to Bit Position 1 and shift Bits 1 through 6 to the left one position.
Figure B.3 illustrates the conversion process for Logical Word
Address 121. Remember that the logical PLC-2 address is a byte address,
so the physical address is also a byte address.
Figure B.3
Converting a Logical Address to a Physical Address
17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00
0 0 0 0
17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00
0 0 0 0
0 0 0 0 1 0 1 0 0 0 1 0
0 0 0 0 0 1 0 0 0 1 1 0