Hardware Considerations
Chapter 2
23
Figure 2.2
Memory
W
rite Protect Jumper
HALFT
ONE WITH CALLOUT
The remaining words in memory from 400
8
to the end of memory,
including data table and user program, are protected and cannot be altered
by programming. The memory write protect feature guards against
unintentional changes to processor memory.
The processor and an industrial terminal can diagnose certain errors
occurring during the execution of the user program which result from
improper programming techniques. For example, it is possible to program
a series of instructions which require the processor to perform an operation
which it cannot do or perform an operation which is defined as illegal
(such as jump to a label that is not located closer to the end of program;
i.e., a jump backwards). These errors become apparent only while the
program is being executed, so are termed run-time errors. If a run-time
error occurs, the processor halts program execution and the PROCESSOR
FAULT indicator illuminates.
The first step in diagnosing run-time errors is to connect the industrial
terminal. It will display the message run-time error in the initial mode
select display. If the industrial terminal is already connected at the time
that a run-time error occurs, the ladder diagram is replaced by the mode
select display containing the error message. Run-time errors can be
detected by the industrial terminal when the processor is in either of two
2.3
RunTime
Errors
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