Re: Unusual Apple // card

[dempson@actrix.gen.nz (David Empson)]

Stephen Shaw <xstephenx@apple2.org.za> wrote:

> On Fri, 22 Mar 2002 11:42:43 +1100, John L wrote:
> 
> > I have obtained an Apple // card whose purpose I can't easily
> > identify.  The card is called "The Micro Works" with the letters
> > "DS-65 (c) 1979" printed directly underneath the title - which is
> > located on the top left of the card.
> >
> > On the card itself are a number of small IC's labeled "74LS85N" and
> > one large IC labeled "F6821P".  There is also an " DS-65 EPROM II"
> > which is socketed as well.  On the top of the card are three trim pot
> > wheels with the letters "B" "C" and "W" respectively labeled above
> > each pot.
> 
> The 6821 is for the 6809 series of processor. The 6809 was similar to the 6502
> so it will work with an Apple. At a guess I'd say it is similar to a 6551 VIA.
> 6821=6551????

You have a few details muddled up there.

The 6821 is a PIA (Peripheral Interface Adaptor), designed for use with
the 6800 family of microprocessors (6800, 6802, 6808, and major
derivatives like the 6801, 6803, 6809 and 68HC11).

The 6502 family was designed to be compatible with the 6800 bus, which
means that 6800 peripherals like the 6821 can also be used with the
6502.

There was a 65xx clone of the 6821, which has a part number of 6520.  It
is also called a PIA.  The 65xx family also has the 6522 VIA (Versatile
Interface Adaptor) which is a functional superset of the PIA with a lot
of extra features.

The 6551 is a serial chip (ACIA = Asynchronous Communication Interface
Adapator).  It is a significantly improved version of the 6850 ACIA.


-- 
David Empson
dempson@actrix.gen.nz