Odp: [sdiy] lpt polyphonic interface

[Roman]

Hi,

your circuit is working on edges rather than stable states.
I mean, when you latch the muh, latched value is changing
at the same moment causing hazards. LPT is suposed to
have RC network at outputs to minimize EMI. That causes
rise/fall times to expand and you really can't say when
and what is written to the latch .
You need a strobe signal from LPT. Your workaround
is the way to do it. Basically, no other bits should change
while latch WRITE is being changed.
But why bother with hardware latch, and not use other
4 bits available in LPT (control register)?

Roman

----- Original Message -----
From: Karl Ekdahl <_nial_ at yahoo.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Friday, November 08, 2002 2:32 PM
Subject: [sdiy] lpt polyphonic interface


> I managed to solve this the software way by doing like
> this:
>
> Set channel 0, (10000000).
>
> Set key 0 to ON (01000000).
> Disable key write but PRESERVE the old key value and
> key state (11000000).
> Change channel to old channel (10000000).
>
> Set key 0 to OFF (00000000).
> Disable key write but preserve the old key value and
> state (10000000).
> Change channel to old channel (10000000).
>
> Set key 1 to ON (01000001).
> Disable key write but preserve the old key value and
> state (11000001).
> Change channel to old channel (10000000).
>
> This works, but isn't especially elegant. Could anyone
> please give me a hint how to prevent the latches to
> write using hardware?
>
> I belive this could have been some comfusing.. :)
>
> /Karl
>
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