Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 87)

6–8 Application Layer Message Packets
Publication 1770Ć6.5.16 - October 1996
ADDR
The ADDR (address) bytes contain the byte address of a memory
location in the command executor where the command is to begin
executing, except in SLC 500 processors, where the ADDR byte is
interpreted as the word address.
In SLC 5/02, SLC 5/03, and SLC 5/04 processors, the CIF
Addressing Mode bit, S:2/8, can be set to a one to change the
interpretation of the ADDR byte to the byte address, so that it is
compatible with other PLC processors. For example, if the
command is to read data from the command executor, ADDR
specifies the address of the first byte of data to be read.
ADDR
contains the low (least significant) byte of the address contains the high byte of the address
Sending commands to PLC-3, PLC-5, and SLC 500 processors
In some instances, when sending commands from the basic
command set to a PLC-3, PLC-5, or PLC-5/250 processor, or to an
SLC 500 processor, you must create special files to accept the data.
Important: The ADDR field specifies a byte address, not a word
address as in PLC data tables. Chapter 13, “PLC
Addressing,” explains how to convert PLC word
addresses to byte addresses. Also, if you use the
“native” read and write commands in PLC-3, PLC-5, or
SLC 500 processors, the address is not a byte address; it
is a logical binary, logical ASCII, or SLC address with
multiple address fields.
SIZE
The SIZE byte specifies the number of data bytes to be transferred
by a message. This field appears in read commands, where it
specifies the number of data bytes that the responding node must
return in its reply message.
The SIZE varies with the type of command. For PLC-5 and
PLC-5/250 typed read and typed write commands, the SIZE field
specifies the number of elements, not bytes. In PLC-5 typed read
and typed write commands, the SIZE field is two bytes long
—transmit low byte first and high byte second.
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