Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 54)

Data Highway Communication
Chapter 3
3Ć9
A PLC–3 station can read from any part of a PLC/PLC–2 data table.
However, A PLC– 3 station cannot write to a PLC/PLC–2 if the switch
settings at the PLC/PLC–2 station forbid access. If the switches at the
PLC/PLC–2 station are set to accept only protected write commands, then
the ladder diagram program at the PLC/PLC–2 station must contain
memory access rungs to define which areas of the PLC/PLC–2 station’s
data table are accessible. In such a case, a transmitting PLC–3 station can
write to only those data table areas defined by the memory access rungs,
and only by means of protected write commands. If the switches at the
PLC/PLC–2 station are set to accept unprotected write commands, a
PLC–3 station can then write to any area of the PLC/PLC–2’s data table
by transmitting an unprotected write command (section titled Command
Message Type chapter 6).
Accessing a PLC–3 from a PLC/PLC–2 Processor
While a PLC–3 processor can address any area of a PLC/PLC–2 data
table, a PLC/PLC–2 reads an input file that is a part of the PLC–3 data
table. That file is the PLC–3 input file with a number that corresponds to
the station number of the PLC/PLC–2 station. For example, the
read/write files assigned to PLC/PLC–2 stations 1 to 100 (octal) would be
as follows:
PLC/PLC-2 Station
Number (octal)
Assigned PLC-3 Input File
for Read/Write Access
000 I008 [1]
001 I001
002 I002
003 I003
004 I004
005 I005
006 I006
007 I007
010 I010
011 I011
012 I012
. .
. .
. .
077 I077
100 I100
[1] Station address 000 is assigned to input file I008. Otherwise PLC-3 input
files with an 8 or 9 in their address are not used for read/write access by a
PLC-PLC-2 station (except I008 for station 0).