A crazy idea

Hi,

Parallel port output CNC programs are limited to 3 or 4 axies because
of the limited number of port bits. Each axis requires a STEP and
DIRECTION bit pair. What if it could be done with a single bit per
axis where STEP and DIRECTION were combined on the same line? It then
would be possible to run 6 to 8 axies.

Here's how it could be done:

(1) 100000000010000000001000... is CW
(2) 011111111101111111110111... is CCW

In (1), a narrow positive going pulse would be interpreted as a CW
motion. In (2), a narrow negative going pulse would result in CCW
motion at the same speed. One would simply invert (1) to generate (2).

This scheme would place no additional burden on the software or on
the bandwidth of the now combined STEP/DIRECTION compared to a
standard STEP pulse line. Decoding hardware in the drive would be
minimal; just a single quad gate package.

So, what do you think, a crazy idea?

Mariss