Have you tried using OPC for this? Connect your Citect's OPC Client to the OPC Server for Modbus (ModNet) and you will get the data you need:
Here is a link to download: http://www.matrikonopc.com/opc-drivers/1603/index.aspx
In order for anyone here to help you, you need to give us more details, such as how have you set up the PLC and scada (RS232/RS485, baudrate, master/slave, cable length etc) and do you get any exception response? Are they both using Modbus RTU?
I managed to get comms between the two using modbus tcp/ip (MODNET). I haven't worked with ABB before so I didn't configure the ethernet port on the cpu correctly. Thanks for your response.