Plcć2 physical addressing, 1774ćplc physical addressing – Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command User Manual
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PLC Addressing
Publication 1770Ć6.5.16 - October 1996
PLCĆ2 Physical Addressing
PLC-2 processors use physical addresses that are directly related to
the logical addresses. To convert a logical address to its
corresponding physical address:
1.
Move bit 7 of the logical address to bit position 1.
2.
Shift bits 1 through 6 to the left one position.
The following figure 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.
Converting a PLCĆ2 Logical Address to a Physical Address
0
0
0
0
0
0
0
0
1
0
1
1
0
0
0
0
Bit (octal)
High byte
Low byte
17
16
11
15
14 13 12
10
7
6
1
5
4
3
2
0
0
0
0
0
0
0
0
0
0
1
1
0
0
0
1
0
Shift bit values 1 through 6
to the left one position.
PLCĆ2 word address = 121 octal
logical byte address = 242 octal
physical byte address = 0046 hex
To send a physical read or physical write to a PLC-2 node, put the
PLC-2 physical address in the ADDR field of the command.
Be sure to encode the low byte of the physical address as the first
byte in the ADDR field.
1774ĆPLC Physical Addressing
The 1774-PLC controllers use physical addresses that are exactly the
same values as the corresponding logical addresses. Remember that
the logical address is a byte address, so the physical address is also a
byte address. For example, the logical byte address of the 17th word
in PLC memory is 32 decimal, and the physical address is 32
decimal.
To send a physical read or write command to a 1774-PLC node,
put the 1774-PLC physical address in the ADDR field of the
command message packet. Be sure to encode the low byte of the
physical address as the first byte in the ADDR field.