Ok guys,

Here are the links to schematics.

ADDRESS DECODER:
http://www.geocities.com/zee_shan5...ecoder.jpg

SERIAL COMMUNICATION BOARD:
http://www.geocities.com/zee_shan5..._Board.jpg

CONTROLLER BOARD (BOARD 1):
http://www.geocities.com/zee_shan5...oard-1.jpg

IO BOARD (BOARD 2):
http://www.geocities.com/zee_shan5..._Board.jpg


Ok, i know wire-wrap has its down sides and negative aspects, but yes i am aware of GROUND and POWER Planes, and i have tried to implement them to every extent possible. I know wire-wrap on Dot-Matrix (Backelite / Fiber) board has very high parasitic capacitance, and maybe this is the reason the design is not working. The reason i started with wire-wrap construction was that this is my first BIG project (involving the use of over 15 or so MSI / VLSI ICs), and i wanted to test it (individual ICs / functions) before placing the PCB order. Secondly, it was not intended to be such a big project in the beginning, and i was supposed to use the more advanced controllers, but as i mentioned, i had to go for the legacy chips (8255s, 8279, etc.) to make this system very easy to understand by freshman students, who are doing or about to enter their Undergrad studies.

Secondly, my friend wanted this to be part of a machine on his factory floor, and it was his restriction to use these components since the original controller systems in his machine were using these parts and that board was destroyed in some major shifting of the plant floor machines, while the manufacturer was not ofering these controller boards separately.

Anyways, thank you all for your expert opinions and advice, and i would really appreciate if someone could trace out the bug(s).

There are 3 boards in this system - 1) Controller board, 2) IO Board and 3) Communication board.

The Address decoder is on the Controller board. The Comm board is connected to teh Controller board by three wires (RX, TX and P1.1). The IO board is connected to the Controller board by 3 data cables 1) Data bus 8-bits, 2) CS decode lines bus 3) RD, WR, A0, A1, RESET bus lines.

Thank you.