Hi,
In one of my application I am planning to put the design on two boards in order to save cost i.e. One 4 layer board containing the micro AT89S53, buffers, supervisor, LCD etc. And other single sided board for 110V AC output modules and 15V DC inputs from proximity sensors, TTL outputs for Stepper motor drives.
I am planning to use the 4 layer board for-
1. MICRO AT89S53.
2. DS1232 Supervisor.
3. 20 X 4 LCD Connector Since I will be using approx. 8 inches cable in between board and LCD should I use a buffer such as 74HC541 to drive this capacitive cable load.
4. A PS/2 Keyboard conenctor.
5. Two 74HC541 on port 0 and port 2 each. port 0 will be used for driving 110 V AC outputs. Port 2 will be used for proximity sensor inputs. I 6 inch cable will run from this 4 layer board to single sided I/O board and hence I am using 74HC541's.

The Single sided board will contain 110V AC outputs and 15 V DC inputs from proximity switches. For 110V AC outputs I will use MOC4081 opto triac drivers and triacs with snubbers put across their output. For Inputs from proximity switches I will use Optocoupler 4N35 the outputs of these opto will go to the buffer on the 4 layer board throu' cable. For driving the TTL +5V logic stepper motor drives I will use optocouplers 4N35.

I want to know is this method of splitting the design ok since I am designing this for and Inustrial application my AIM is to keep good EMC. and EMI low.
Please provide me your valuable suggestions and comments.
Thank you all.

Regards,
Prahlad Purohit