Run out of Ports

[victorf]

I have a legacy product that I built and sold back in the late 80s and throughout the 90s. It was built around a MicroMint BCC-52 micro controller. Interfaced to the controller were two rotary shaft encoder with counts of 2048 or 4096 per revolution. These encoders were interfaced to a pair of HCTL-2000 quadrature decoder/counter interface ICs. Without going into detail, the -52 periodically read the counts of the two encoders and used that information to determine the azimuth and elevation angles of the telescope they were attached to.

Most of these systems are quite obsolete but have stood the test of time. Many are still working as designed. However I am starting to get calls from owners who are looking to upgrade their units. Since the telescope device is the most expensive and robust part of the system, I have been giving thought to simply replacing the controller hardware with
something a bit more modern and plug compatible with the telescope. I am considering a ZX-24. I find that I can still get the HCTL-2000 interfaces.

Each of these ICs outputs the current encoder counts as a pair of 8 bit words which means that I will have to use 8 I/O ports to read each -2000. I cannot afford to use 16 I/O ports as some will be needed to attend to other functions. Is there any solution to this dilemma?

Vic

[twesthoff]

Each of these ICs outputs the current encoder counts as a pair of 8 bit words which means that I will have to use 8 I/O ports to read each -2000. I cannot afford to use 16 I/O ports as some will be needed to attend to other functions. Is there any solution to this dilemma?

Vic

Yes, theHCTL-2000 chips have tri-state outputs so you can parallel the D0-D7 outputs of both chips on one controller port. Then use 2 other I/O pins to select the chip you want with the ~OE pins (or 1 extra pin and an inverter). Fairly easy to do...
I can give you more specific help offline if you wish.
Tom W.

[dkinzer]

I cannot afford to use 16 I/O ports as some will be needed to attend to other functions. Is there any solution to this dilemma?

You could use a 40-pin or 44-pin ZX device. Alternately, AN-213 External Device Interfacing contains several ideas for expanding the number of available I/O pins.