Hi, I am a 4th year electrical engineering student, currently involved in my senior project. As part of my project I need to connect an Allen Bradley PLC-5 with a PC to exchange data. On PLC side I am using ASCII Read block to read data from the PC. On the PC side I am using Visual Basic MSComm control to sent data to the PLC. The cable (null modem) is connected from the COM port of the PC to the Channel 0 (serial port) of the PLC-5/11. From the past experience and reading I understand that channel 0 of the PLC-5 uses RS-232 protocol to transfer data. If that is correct then it should be receiving the data being sent through the COM port of the PC. But for some reason PLC doesn't seems to be accepting any data through channel 0. Can anyone tell me what's wrong with this set up and what do I need to do to correct this problem? Right now I am doing the on-line programming changes to the PLC through the channel 0. Once I do the changes I change ch.0 mode to 'user' so that it can read data being sent by VB application. Once I change ch.0 mode to 'user' I'll loose the on-line connection with the PLC. So right I am using ch.0 for both on-line programming and data exchange. May be this is causing any problem? I had to do like this because I don't have a KTX or PCMK network card to get on-line with PLC. As a student I can't effort to buy those network cards for $700 (even a used one). Can anyone please tell is there any inexpensive way to get online with PLC other than through ch.0 so I can leave ch.0 for data exchange only? Anyone kind of help on this issue is greatly appreciated! Thank you in advance!