Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual User Manual
Page 152
Data Encoding and Addressing
Chapter 6
6-15
PLC
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 will also be a byte address. For
example, the logical byte address of the 17th word in PLC memory is
32 decimal, and the physical address of that word is also 32 decimal.
To send a physical read or write command to a PLC station, put the PLC
physical address in the ADDR field of the command message format
(Chapter 5). Be sure to encode the low byte of the physical address as the
first byte in the ADDR field.
PLC-2
PLC-2 controllers use physical addresses that are directly related to the
logical addresses. 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 6.10 illustrates the
conversion process for Logical Word Address 121. Remember that the
logical PLC-2 address is a byte address, so the physical address will also
be a byte address.
To send a physical read or write command to a PLC-2 station, put the
PLC-2 physical address in the ADDR field of the command message
format (Chapter 5). Be sure to encode the low byte of the physical
address as the first byte in the ADDR field.
Figure 6.10
Converting PLC-2 Logical Addressing to Physical Addressing
PLC-2 Word Address
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
Logical
Bit Number
(Octal)
Byte Address
=
121 Octal
242 Octal
0046 Hex
=
=
Logical Byte Address
Physical Byte Address
17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00
0
0
0
0
0
0
0
0
0
1
0
0
0
1
1
0
Physical
Byte Address
High Byte
Low Byte
11397
Bit Number
(Octal)