Rockwell-automation 1770-KF2 Data Highway or Highway Plus Interface Mo Manual de usuario descargar pdf (Pagina 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 W

ord

Address

17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00

00 00

00 0010100010

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

00 0000 0001000110

Physical

Byte

Address

High Byte Low Byte

11397

Bit Number

(Octal)

1 2 ... 147 148 149 150 151 152 153 154 155 156 157 ... 234 235

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