Rockwell Automation 1771-KA2 Communication Adapter Module - Manual (Page 41)

Commands
Chapter 4
4-5
A write command can control data table words at any station processor.
However, certain data table areas at each type of processor have a special
function and should not be controlled by write commands. (Sections
titled “Accessible Data Table Locations-PLC-2 Processors” and
“Accessible Data Table Locations-PLC Processors” cover data table
control.)
Bit write commands control the ON/OFF status of bits in a remote station
data table. Unlike read or write commands, bit write commands do not
transfer data table memory data. Instead, the programmed command rung
itself specifies which bits are to be set on or off when the command is
executed. (Refer to chapter 5.)
There are 2 types of bit write commands that can be sent from a
communication adapter module:
Protected bit write
Unprotected bit write
The distinction between these commands is their memory access.
Protected bit write commands are not executed by the receiving station
unless a memory access rung defining the appropriate memory area is
programmed at that station and switch 1 is set. Because this write
protection feature allows added control over command execution, use of
protected commands is recommended.
A bit write command can control data table areas at any station processor.
However, certain data table words at each type of processor have a special
function and should not be controlled by bit write commands. (Data table
control is the subject of sections titled “Accessible Data Table
Locations-PLC-2 Processors” and “Accessible Data Table Locations-PLC
Processors”).
On each 1771-KA2 communication adapter module, the sending and
receiving of write messages can be enabled or disabled by switch settings.
(Refer to chapter 3.)
Bit Write Access
The bit write command can be used to control any accessible data table
bit. However, this command must not be used to control the following:
Any bit whose status is controlled by a programmed output instruction.
Any bit in a byte that also contains program-controlled bits.
Bit Write Commands