Expansion Base Output Hold Option
The bit settings in V–memory registers V7741 and V7742 determine the expansion bases’
outputs response to a communications failure. The CPU will exit the RUN mode to the
STOP mode when an expansion base communications failure occurs. If the Output Hold bit
is ON, the outputs on the corresponding module will hold their last state when a
communication error occurs. If OFF (default), the outputs on the module unit will turn off
in response to an error. The setting does not have to be the same for all the modules on an
expansion base.
The selection of the output mode will depend on your application. You must consider the
consequences of turning off all the devices in one or all expansion bases at the same time vs.
letting the system run “steady state” while unresponsive to input changes. For example, a
conveyor system would typically suffer no harm if the system were shut down all at once. In a
way, it is the equivalent of an “E–STOP”. On the other hand, for a continuous process such
as waste water treatment, holding the last state would allow the current state of the process to
continue until the operator can intervene manually. V7741 and V7742 are reserved for the
expansion base Output Hold option. The bit definitions are as follows:
Bit = 0 Output Off (Default)
Bit = 1 Output Hold
WARNING: Selecting “HOLD LAST STATE” means that outputs on the expansion bases will not be under
program control in the event of a communications failure. Consider the consequences to process
operation carefully before selecting this mode.
DL205 User Manual, 4th Edition, Rev. B
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Chapter 4: System Design and Configuration
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D2–CM Expansion Base Hold Output
Expansion
Base No.
V–memory
Register
Slot 0
Slot 1
Slot 2
Slot 3
Slot 4
Slot 5
Slot 6
Slot 7
Exp. Base 1
V7741
Bit
0
1
2
3
4
5
6
7
Exp. Base 2
8
9
10
11
12
13
14
15
Exp. Base 3
V7742
Bit
0
1
2
3
4
5
6
7
Exp. Base 4
8
9
10
11
12
13
14
15
