| Citect will read extra address ranges when
it will improve performance to the PLC. In your case Citect reads
digital addresses in blocks of 16. So if you have a digital tag at
C1000, Citect will read from C993 to C1008 in a single request. If
the address C993 does not exist then you will get the Address is
out of Range error. Because of this optimisation of digital read
requests you should make sure that these are valid addresses in the
PLC. In some PLCs you can setup the valid ranges of all memory
addresses and you should make sure the setup in the PLC is what
Citect is going to read. If you cannot adjust the range then you
should not use any digital tags within the first and last 16
digitals.
Citect also try's to block reads together and may try to read
across invalid addresses. For example if you configure C1000 and
C1100, Citect will try to read from C993 to C1105. If any address
is invalid between these tags you will also get and Address is out
of range error. This is quite unlikely as almost all PLC contain
continuous memory with no holes.
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