Path: utzoo!mnetor!uunet!cbmvax!grr
From: grr@cbmvax.UUCP (George Robbins)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Question about 8520 CIA chips
Message-ID: <3688@cbmvax.UUCP>
Date: 24 Apr 88 17:15:48 GMT
References: <11419@tut.cis.ohio-state.edu>
Reply-To: grr@cbmvax.UUCP (George Robbins)
Organization: Commodore Technology, West Chester, PA
Lines: 41

In article <11419@tut.cis.ohio-state.edu> erd@tut.cis.ohio-state.edu (Ethan R. Dicks) writes:
> 
> I looked at the differences internally between the 6526 CIA and the 8520 CIA, 
> and found that the only difference is in the TOD clock, one is BCD and the
> other is binary.  I also found by looking in my AW RKM hardware manual that
> the TODs are used for the timer.device for 60Hz and millisecond event timers

The changes addressed were as follows:

1) Change TOD counter to a binary counter w/o divide by 5/6 prescaler,
   including some timer bit shuffling.

2) Resolve the 6526 problem where interrupt request bits are set and can
   thus be unintentionally cleared one cycle prior to setting the overall
   interrupt request flag.

3) Provide additional delay on PC pin to meet Centronics setup/deskew spec.

4) Tighter specification of bus interface timings to match 68000 vs 6502 specs.

5) Auto-start of timers set for one-shot mode.

6) Specification of minimum timings for F and CNT inputs.

> I assume that there is not a version of the 6526 which can be stuck directly
> on the 7.1 MHz Amiga bus, but am I wrong?  Are the pinouts the same?  (I could
> not find an 8520 pinout in _my_ literature, but then I don't have the A1000
> schematics)  If you could stick a 6526 in the 8520 slot, how could you
> replace the timer.device with one which understands a BCD timer?  Note:  I
> am not asking how to manipulate BCD with a 68000, but how to change a device
> driver which is _not_ disk resident.

The pinout is the same and the various timings are probably good enough to
slip by in most cases, however I wouldn't expect the software to work correctly
if the two interval counters don't operate in the expected manner.  It might
limp along rather than croaking instantly, but I wouldn't bet on it...

-- 
George Robbins - now working for,	uucp: {uunet|ihnp4|rutgers}!cbmvax!grr
but no way officially representing	arpa: cbmvax!grr@uunet.uu.net
Commodore, Engineering Department	fone: 215-431-9255 (only by moonlite)