Re: Homebrew STG card

[Jon Elson <jmelson-at-artsci.wustl.edu>]

Matt Shaver wrote:

> Yes, the timer outputs are to be the step signals. There isn't any
> requirement for an interrupt. The clock inputs (3 for each 8254) need to be
> driven from one of those metal oscillator modules (one module drives all
> three 8254s together), probably at 1MHz. The gate signals (3 for each 8254)
> will probably need to be pulled up (or down, I forget which) to enable
> continuous counting. A small scratch area would be nice, but I'll try to pin
> down the exact requirements by experimenting with a prototype card I have.
> The main issue with the gate signals is whether we can set the output
> frequency to zero by programming the 8254,

Yes, you can, but it might cause a glitch in the output when you reprogram
it.  It might be possible to set bits in a sequence to avoid this.
Also, you could arrange that the counter can be set slower than the
time between program update cycles.  If there will be no pulses to generate
this program cycle, it sets the count longer than the update rate, and updates
the counter every cycle, to keep putting off the next pulse.

Jon