Hardware Considerations
Chapter 2
24
modes, program or remote program. (If the keyswitch is in
RUN/PROGRAM position, the industrial terminal automatically puts
the processor into remote program mode. If the keyswitch is in the RUN
position, or when it is connected to the processor through the 1771-KA2
communications adapter module, you must manually change the keyswitch
to the PROGRAM position).
WARNING: Forces are immediately removed if a Run-time
error occurs.
After returning the industrial terminal display to ladder diagram mode by
pressing [1][1] in mode selection operation, the industrial terminal displays
the instruction that caused the error with a message describing the run-time
error.
After you have corrected the run-time error by editing the user program,
the processor can be restarted by switching to the run or run/program
mode.
Five indicators are located on the front of the processor (Figure 2.1). You
should become familiar with these indicators.
MEMORY FAULT — Illuminates when an error in the parity of data
retrieved from memory is detected. Changing the mode select switch to
the PROG position or cycling line power may clear this fault condition.
Reloading the program may also clear the fault.
BATTERY LOW — When the batteries for memory back-up are low,
this red indicator flashes on and off. Alkaline batteries will continue
to back up memory for about one week after the BATTERY LOW
indicator begins to flash. Lithium batteries have a longer life, but are
essentially dead when the indicator flashes. Regular replacement of
the batteries is recommended: for alkaline, every 6 to 12 months; for
lithium, every 2 years. (See the Assembly and Installation manual for
replacement details, publication no. 1772-6.6.2.)
The low battery bit, bit 027/00, will cycle on and off when a low battery
voltage condition is detected and the mode select switch is not in the
PROG position. Programming techniques can be used to examine this
bit and to control some type of alerting device when a low battery
condition exists.
2.4
Processor Diagnostic
Indicators
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