Magnus Danielson cfmd at
Tue Aug 8 00:11:18 CEST 2000

From: buchi at (Michael Buchstaller)
Subject: Re: MOS6581
Date: Mon, 07 Aug 2000 19:27:11 GMT

> >scavenging.  Also, there's a different version of the 6581 in later 
> >C64s(?)... I can't remember the number right now, but it has slightly 
> >different voltage requirements than the 6581.  
> That´s the 6582. I think it needs a 2nd power supply of 9 V instead
> of the 12 V in the 6581.
> I have been thinking of hooking a 6581 to my PC´s parallel port
> (Data lines to PP data lines, Address lines to the control lines)
> Does anybody know if the 6581 is very picky about signal levels
> (will i have to buffer the signals ?)

As it happends, I still have my Commodore 64 Programmer's Reference Guide which
in the back holds what could be considered to be datasheets as well as the full
schematics of the C-64. It was actually floating around on the top of things,
so it was a easy grasp to answer your question. Now, in there is the following
taken from the Electrical Characteristics:

Characteristics     Pins	       Symbol  Min  Typ  Max  Units
Input High Voltage  Res, 02, R/W, CS,  Vih     2     -   Vcc  Vdc
Input Low Voltage   A0-A4, D0-D7       Vil    -0.3   -   0.8  Vdc

Thus, very standard TTL levels.

If you are unsure, drop in a 'HC240/244 to buffer Res, R/W, CA and A0-A4 and
a 'HC245 to buffer the D0-D7. Also please note that you must supply the clock
signal since this form the basis of the VCO frequency tracking. It's really a
24 bit phase-accumulators in there where you are able to program only the lower
16 bits.

One of the things I recall that I do like about this design is its ring and
sync features. Also, since the frequency settings is in linear frequency you
can do linear frequency modulation (in software) if you so wishes. They surely
knew how to cram a lot of stuff in the chips back in those days. Not many
modifications away and people would _really_ consider this a powerfull chip.

Hmm... wounder if I could mimic it in VHDL ;D

Magnus - still a C-64 owner after all these years

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