Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 231)

13–16 PLC Addressing
Publication 1770Ć6.5.16 - October 1996
PLCĆ5 Physical Addressing
PLC-5 processors use physical addresses that are related to logical
addresses by means of pointers. Since no two PLC-5 systems are
configured identically, the pointers are not fixed. Therefore, there is
no algorithm for converting logical to physical PLC-5 addresses.
A PLC-5 physical address goes in the 4-byte field labelled PLC-5
PHYSICAL ADDR in the PLC-5 physical read or write command
message packets. A physical address is made of 24 bits. These bits
are inserted in the message packet physical address field as follows
(bits are labelled A1 to A24 respectively):
Function (FNC) Field
First byte A8 A7 A6 A5 A4 A3 A2 A1
Second byte A16 A15 A14 A13 A12 A11 A10 A9
Third byte A24 A23 A22 A21 A20 A19 A18 A17
Fourth byte 0 0 0 0 0 0 0 0
Size Field
For example, to address a command message to physical word
address 12,200 decimal (002FA8 hex), use the following binary code
in the address field:
First byte 1 0 1 0 1 0 0 0 (value A8 hex)
Second byte 0 0 1 0 1 1 1 1 (value 2F hex)
Third byte 0 0 0 0 0 0 0 0 (values 00 hex)
Fourth byte 0 0 0 0 0 0 0 0 (always 00 hex)
The recommended procedure for uploading or downloading PLC-5
memory is to begin at physical address 0000 and proceed
sequentially to the end of memory. Therefore, each successive
physical read or write begins at the next physical address after the
one where the previous command stopped. Since a single physical
read or write command can transfer only about 120 words of data,
it takes many commands to upload or download the entire PLC-5
memory.