Applies To:
  • CitectSCADA 1.00 1.01 1.10 1.11 1.20 2.00 2.01 3.00

Question: I am getting a PLC hardware error "Address is out of range". When I look in the SYSLOG.DAT file it shows that the address in question is C993. However I am not using this address in any of may tags. Why is Citect reading this address? 

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.