
This is an explanation of the cross talk test board.

Basic Circuit:

The basic circuit is 32 lines be driven by 74AS00's and received by
74AS245's.  the lines run in parallel for 8 inches.  By-pass capacitors
are distributed as close as they can be placed together along parallel
lines.  Every other capacitor should be connected to VDL and +5.  Put a
row of capacitors behind these that connects between VDL and +5.  The
32 bit bus signals are 8 mils and are on a 25 mil pitch.

By-pass each IC.


Layer Assignment:

The board is 10 layers.  Layers 2 and 9 are ground.  Layer 5 is +5.
Layer 7 is VDL.


Circuit 1:

Run the 32 bit bus on layer 3.  Cross the bus near the center with 8 traces
ranging in length from one inch to 4 inches.  The longer traces can bend.
Put a test point on each end of the traces with a ground test point .1 inches
away.


Circuit 2:

Run a basic 32 bit bus on layer 1.


Circuit 3:

Split the 32 bit bus into four 8 bit busses and run these directly over the
top of each other on layers 3, 4, 6, and 8.

             -  -  -  -  -  -  -  -  -     layer 3
             -  -  -  -  -  -  -  -  -     layer 4
                   +5
             -  -  -  -  -  -  -  -  -     layer 6
                   VDL
             -  -  -  -  -  -  -  -  -     layer 8


Circuit 4:

Split the bus into two 16 bit busses and have them overlap as shown below:

      - - - - - - - - - - - - - - - -
                     - - - - - - - - - - - - - - - -
This is on layers 3 and 4.


Circuit 4:

Repeat circuit 1 except make the busses with about 33 mil pitch.


Circuit 5:

Repeat circuit 3 except make the busses with about 33 mil pitch.

