This directory contains schematics, printed-circuit board layouts and
assembly drawings for an adapter to connect a PC Parallel Printer Port
to a Motorola Background Debug Mode (BDM) port.  The circuit is a slight
modification of `5-chip BDM Interface' available from several Web sites.
The modification, which adds a single resistor and capacitor between
two sections of the 74HC132, eliminates a race condition that causes
glitches on the CPU32 BERR* line.

Motorola provides schematics for a `2-chip BDM Interface' which may also
be used with the Linux BDM device driver.  I have found this `2-chip'
circuit to be more prone to noise and timing problems.  The circuit
described here works reliably on a 266 MHz Pentium machine even with
the delay value set to 0.  This is a considerable improvement over the
`2-chip' circuit.

One of the most important things to consider when building the circuit is
keeping the grounds of the PC, the BDM interface circuit, and the
CPU32 system all at the same value.

The weakest link in the chain is the single ground wire on the 10-pin
ribbon cable between the BDM interface and the 68360 system.  For best
results keep this cable as short as possible.  If you can get ribbon
cable with an overall shield, use it with the shield hooked to pin 5
on the 10-pin plug at one end and to the ground of the BDM interface
circuit at the other.

I used `twist-n-flat' ribbon cable for both the BDM and printer port
connections.  An equally good solution for the printer-port cable would
be overall shielded twisted pair.

I made the cable to the printer port about 2 meters long and the BDM ribbon
cable about 40 cm long.  As noted above, I am able to run the driver with
a delay of 0 on a P266 machine.
