Posted By
candle
on 2019-06-14
21:16:39
|  sid card sid frequency
I've been looking around for some clues on how sid is clocked on sid cards, and it seems it uses just mux signal passed through flip-flop making it 50% of 1.7mhz and then, to sync back writes to cpu actual frequency some glue logic is used
is there more to it? reads are required? (no biggie, since busy signal is presend on the cart bus)
is there more than one base address? it seems that there was quite a few variations for such card
also - links for documentation do not work anymore, any one has a copy?
http://plus4world.powweb.com/hardware/Solders_SID_Card
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Posted By
Luca
on 2019-06-15
02:20:24
 | Re: sid card sid frequency
That link's gone forever, I swapped it with the circuitry's GIF.
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Posted By
candle
on 2019-06-15
04:36:26
| Re: sid card sid frequency
thanks!
writes & reads looks like hit & miss - if you happend to access sid when cpu is working in 1.7mhz mode chances are it will fail
is there any software workaround about this or something?
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Posted By
gerliczer
on 2019-06-15
05:45:44
| Re: sid card sid frequency
Solder's SID card runs on half the system clock, supports no register reads (AFAIK) and you synchronize access by setting the CPU clock to slow (read TED documentation).
BSZ's card (http://plus4world.powweb.com/hardware/NSTs_Audio_Extension_V2_0) can be programmed to run on half the system clock or C64 clock, supports register reads without tricks and there's still some slight chance that more will be build. It has complete documentation.
Also there is the one made by Scala (http://plus4world.powweb.com/hardware/Scalas_SIDcard). I think this has all documentation, so you may even build one yourself.
There were another cards made by Csory, a Hungarian guy called MotoHacker and probably some others.
Base address is $FD40 for Solder's cards and $FE80 for Csory's (AFAIR). BSZ's supports both.
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Posted By
candle
on 2019-06-15
09:06:53
| Re: sid card sid frequency
thanks for pointing this out
c64 mode is just for *.sid playback or it's actually used in native software?
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Posted By
siz
on 2019-06-16
06:39:48
| Re: sid card sid frequency
As I recall only the first few prototype SIDCards required switching to single clock. The "widely" spread versions didn't need that. And they also listened to both $fd40 and $fe80 addresses.
As these SIDCards used TED single clock (886kHz for PAL) they sound a bit different (lower frequency) compared to the C64 for the same tune.
The NST SIDCards (and according to BSz no, probably there won't be a new batch of these) use the same frequency for compatibility reasons but can be switched to original C64 frequency. Some of the SID players (like SIzPlay and SD2IEC SID Player V2) use these feature the allow listening to C64 tunes in original form.
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