On Sat, 22 Nov 2003 ragge@ludd.luth.se wrote:

> > Does anyone know the CSR address(es) for the built-in AM79C30A
> > audio/ISDN chip on the VAXstation 4000/VLC and the 4000/60?
> >
> Yes, on the /60 it is supposed to be at address 0x200D0000.
> I think it is addressed byte-wise on longword addresses, or something.

<grin>

Oh good!  Based on examining a few of the most likely memory addresses
on my 4000/VLC late last night, this is actually where I was guessing it
would be located.  Specifically, the address range from 0x200D0000-
0x200D001C looked to be the most promising.  It'll be helpful to work
under the assumption that it's to be accessed as bytes on the longword
boundaries since that reduces the number of bytes I have to look at to
only eight.

The AM79C30A itself only needs two bytes for it's I/O and control
interface, one 8-bit data register, another 3-bit value to select one of
its internal registers, and then 5 other bits for read, write, chip
select, interrupt, and reset--but I imagine DEC may have assigned some
of the individual bits to whole bytes in memory for convenience.  So,
the interesting part will be figuring out precisely how it's mapped into
that address range.

-brian.