Applies To:
  • CitectSCADA x.x

Question: How many protocols can Citect use simultaneously? 

There is no limitation on the number of protocols Citect can use simultaneously. Citect does have a limit to the maximum number of Units it can communicate. This limit is currently 1024 in Version 2.10 (4096 in version 4.20 and later), so in theory Citect could use 1024 different protocols at the same time. This may not work in practice as your computer will start to run out of slots, interrupts, io ports and memory addresses which are used by the hardware interface cards. You can use multi I/O Server computers to help work around these hardware restrictions. However it is good to know that Citect does not provided any restriction to the number of simultaneous protocols.

If you are using serial protocols there is a limitation on the maximum number of serial channels supported by the COM port and Digiboard drivers as follows :

COMX Maximum of 9 serial channels in Windows 3.x or 256 serial channels with Windows NT.
COMXI Maximum of 4 Boards of 4 Ports each to give total of 16 serial channels.
PCXI Maximum of 7 Boards of 16 Ports each to give total of 112 serial channels.
MCXI Maximum of 4 Boards of 8 Ports each to give total of 32 serial channels.

These limitations are imposed by the physical hardware as you cannot put more than this many boards in a single computer. You will run out of memory addresses or interrupts. You may get more serial channels by using a second I/O Server. For example you could install 4 PCXi 16 channel Digiboards in each of 3 I/O servers to give a total of 192 serial channels. In this way you can have virtually unlimited number of serial channels supported.

Citect version 4.x and later uses the native Windows NT or Windows 95 serial drivers to provide up to 256 serial channels. As Citect uses the Windows driver you are not limited to using Digiboards for high performance requirements. This would allow you to exceed the maximum of 112 serial channels with a PCXI Digiboard.