Rockwell Automation 1785-LTx,D17856.2.1 Classic PLC-5 Programmable Controllers Users Manual - Manual (Page 92)

Selecting Interrupt Routines
Chapter 7
7-10
Setting PowerĆUp Protection
You can set your processor so that after a power loss the processor does not
come up in run mode. Bit 1 in word 26 of the processor status file sets
power-up protection. Table 7.I shows the states for this bit.
Table 7.I
Setting and Resetting the PowerĆUp Protection Bit
If word 26, bit 1 Is: After power loss, the processor:
Set (1) Scans the fault routine before returning to normal program scan
Reset (0) Powers up directly at the first rung on the first program file
Set word 26, bit 1 manually from the processor status screen (see the
chapter on using status data in programming software documentation). Or
you can latch this bit through ladder logic. When set, the processor scans
the fault routine once to completion after the processor recovers from a
power loss. You can write the fault routine to determine whether or not the
processor’s current status permits the processor to respond correctly to
ladder logic—i.e., whether to allow or inhibit the startup of the processor.
Allowing or Inhibiting Powerup
Bit 5 of status word 11 indicates whether or not you want to power up the
processor after a loss of power. After a power loss, the processor
automatically sets this bit; Table 7.J shows how you can change it from
your fault routine.
Table 7.J
Setting and Resetting the Startup Bit
If the fault routine
makes word 11, bit 5:
Then the processor:
Set (1) Faults at the end of scanning the fault routine.
Leave this bit set to inhibit startup.
Reset (0) Resumes scanning the processor memory file.
Reset this bit to allow startup
Important: You can use JMP and LBL instructions to scan only
the portion of the fault routine associated with a particular fault or
power-up condition.
For information about startup protection on SFCs, see the programming
software documentation set.