Rockwell Automation 2706-MB1 MESSAGEVIEW 421 SOFTWARE MANUAL - Manual (Page 72)

4–24 Planning an Application
Publication 2706-817
Toggling a Maintained Function Keys
The procedure for toggling a Maintained Function key depends on
whether the initial message is in Jog or non-Jog mode.
To return the Function key’s associated bit to its former state:
•
If the message is in jog mode, the operator may press and release
the Function key a second time. If the operator continues to press
and release the Function key the associated bit will be toggled.
•
If the message is in non-jog mode, a second message that has the
same Function key enabled must be triggered. It tells the operator
to press and release the Function key.
Latched Function Keys
A Latched Function Key changes state (0 to 1 or 1 to 0) when
pressed, and remains in the changed state when released. It does not
unlatch if it is pressed again. A Latched Function Key returns to its
original state only when the logic controller sets the latch handshake
bit.
For the procedure when the controller is an ASCII Triggering device,
see Page 4–22.
A Latched Function Key retains its latched state after the message is
terminated. After a terminal reset or powerup, the initial state of a
Latched Function Key is always its released state.
A Latched Function Key requires a handshake tag. The handshake
tag unlatches the Function key when the bit at the handshake tag
address is set to 1 by the logic controller.
Handshake Bit = 0
Write Tag Bit = 0
Function Key
Pressed Function Key
Initial State Controller Program Sets
Handshake Bit = 0 Handshake Bit = 0
Handshake Bit to 1
Handshake Bit = 1
Controller Program Sets
Handshake Bit to 0
OFF ON ON OFF
Function Key
Released
Write Tag Bit = 0 Write Tag Bit = 1 Write Tag Bit = 1
!
ATTENTION: If communication with the logic
controller uses Remote I/O protocol with block
transfer, the Function key write tags must all be
assigned to the same block as the Function Key Return
Message Number tag.