Applies To:
  • CitectSCADA 5.xx, 6.xx, 7.xx
  • CitectHMI 5.xx, 6.xx, 7.xx

My I/O Device has limited I/O (in this case 12 digital inputs) but the MODNET driver reads a 16-bit block of registers, resulting in #COMs and a "Address is out of range" hardware alarm.

I also get an error in the kernel/syslog.dat:

Tue Apr 24 09:54:53 2007 01:58:11.293 Error: Address is out of range
READ 0001 PORT1_BOARD1 IODev 100001 16
Generic 000001 Driver 00008194 (0x00002002)


Because the MODNET driver will block its read requests by default, you will need to add a 'G' prefix to all variable tag addresses that you do not want blocked. For example, to have register 40001 read on its own, the variable tag address should be set to G40001.

Please ensure that you are using MODNET driver V2.05.12.005 or above, as older versions of the MODNET driver do not support the 'G' prefix addressing.

Note: If a register of an I/O Device is addressed with a 'G' prefix, the other registers can still be addressed using standard MODNET addressing.