Applies To:
  • CitectSCADA 5.xx

I have a Digiboard and I would like to know more about it. 

First please read articles Q1825, Q1934, Q2095, Q2150.

Background Information
Digiboards that are used commonly with Citect are the Com/Xi, PC/Xi, and PC/Xe. The Com/Xi and PC/Xi are now discontinued products that are replaced by the PC/Xe. However all work equally well with Citect under NT 4.0.

Drivers for the PC/Xi and PC/Xe are supplied by Microsoft in NT 4.0. (This article will ignore any issues with Windows 95 as it is really a toy and you should always use NT for anything important) There are no supplied drivers for the Com/Xi card in NT. This means that you must use the Citect driver as detailed in Q2095.

The Com/Xi card comes in 3 different flavours. RS232, RS422, and a combination of RS422/RS485.
The PC/Xi card comes in RS232 or RS422.
The PC/Xe card comes in RS232 or RS422.

You can identify the card you have by checking either Digiboards Web site at or article Q1967.

The hard part is to identify the cable to use. I have not been able to find any information on the pinouts of the 78 pin D connector typical of the Digiboards. However by examining the available pins on the 25 pin cables you can make an educated guess at the cable you have.

The pinouts for the RS232 cables are:

Signal Description DTE Use DCE Use DB-25 Pin DB-9 Pin
GND Chassis ground N/A N/A Shell Shell
TxD Transmitted Data Output Input 2 3
RxD Received Data Input Output 3 2
RTS Request to Send Output Input 4 7
CTS Clear to Send Input Output 5 8
DSR Data Set Ready Input Output 6 6
SG Signal Ground Reference Reference 7 5
DCD Data Carrier Detect Input Output 8 1
DTR Data Terminal Ready Output Input 20 4
RI Ring Indicator Output Input 22 9

The pinouts for the RS422 cables are

Signal Description DB-9 Pin DB-25 Pin
TxD+ Transmitted Data (+) 8 2
TxD- Transmitted Data (-) 9 14
RxD+ Received Data (+) 6 3
RxD- Received Data (-) 7 16
RTS+ Request To Send (+) 2 4
RTS- Request To Send (-) 3 19
CTS+ Clear To Send (+) 4 5
CTS- Clear To Send (-) 5 13
GND Chassis Ground Shell 1 7

From this you can pick the 25 pin cable and determine if it is for an RS232 or RS422 board. The pins that are used are the only ones available. So on a 25 pin RS232 connector from Digiboard you will only have Pins 2,3,4,5,6,7,8,20,22. The RS422 cable will have pins 2,3,4,5,13,14,16,19.

You can also tell from looking at the 78 pin connector on a 4 port cable if it is 232 or 422. The RS232 cables will have all their pins on the right hand half of the connector. The RS422 cable has all its pins on the top half of the connector.

PC/Xi and PC/Xe

To install the PC/Xe or PC/Xi in NT 4.0 you install it as a Network Adaptor. The drivers that come with NT will automatically map all the ports as Com Ports starting from the first available port. To then utilise these ports in Citect you access them as standard Com ports with the COMX driver and specify the appropriate port number in your Ports form. This will also leave any other ports available for use by other programs within NT.


To use the Com/Xi card with Citect under NT 4.0 you do not install any other software. Citect supplies its own driver to communicate with the Com/Xi cards. Set this up as per the help. The following is an example of the information in the Communication/Boards form.

Name : B1
Address: 0xD000
IO Port: 0x320
Interrupt: 5

Citect will use the WinRT driver to talk to the Com/Xi card. What this means is that the WinRT Device will not be installed and running before you try and start Citect running. You will get an error message the first time you try and run Citect. Citect at this point will tell NT everything it needs to know to install the WinRT device Driver, but you will have to Shutdown and Restart NT for the WinRt device driver to take effect.

Testing your Installation

The best way to test any Serial Comms is to use the Loopback protocol. Check article Q1684.

To do this test with RS232 you just have to put a jumper between pins 2 and 3. For RS422 you need to connect RX+ to TX+ and RX- to TX- or in the case of Digiboards and 25 pin connectors that would be pins 2 to 3 and 14 to 16.

Good Luck.