User Manual PLC-3 FAMILY I/0 Instruction Manual

DH and DH+ Communication
Chapter 4
4-10
PLC-2 Stations
For communication with a PLC-2 station, write access privilege depends
on switch settings at that remote station. For an explanation on how to set
the switches for write access, refer to the Communication Adapter Module
User’s Manual (publication 1771-6.5.1).
Accessing a PLC-2 Station
Access to a PLC-2 station also depends on the type of command
transmitted to that station. There are two types of commands:
protected write commands –– can only write to specified sections of
the data table in a PLC-2 processor. Memory-access rungs in the PLC-2
ladder program specify where in the data table the PLC-3 can write data.
unprotected read and write commands–– can read or write to any
section of the data table at a PLC-2 station. Refer to publication
1771-6.5.1 for an explanation of protected and unprotected commands
and memory access rungs.
A PLC-3 station can read from any part of a PLC-2 data table. However, a
PLC-3 station cannot write to a PLC-2 station if the switch settings at the
PLC-2 station do not allow access.
If the switches at the PLC2
station are set to accept only:
then a PLC3 station can write
to the PLC2 data table in:
by transmitting:
protected write commands memory areas defined by the
PLC2 ladder program
protected write
commands.
unprotected write commands any area of the data table unprotected write
commands.