On Wed, Mar 05, 2008 at 05:35:05PM -0500, Sridhar Ayengar wrote:
I was planning on using an 8-bitter with a couple-K of
RAM built-in and
a built-in IDE interface.
I've built and maintained 68000-based Unibus, Qbus, and VAXBIcommunications
boards (not like anything DEC ever made, so we were free to/had to write
all of our own drivers for RSX, RSTS, VMS, and Ultrix). Given that the
IDE interface wants to be 16 bits, and given that the bus interface is
16 bits for Unibus and Qbus, a) that's a lot of I/O pins for an
integral MCU, and b) it might take some external hardware to have an
8-bit CPU passing data between two 16-bit pipes (latches, or some way
to handle a measurable delay between writing the top half and bottom
half of your data.
We had to resort to some tricks to interface a 16-bit CPU to the 32-bit
VAXBI BIIC interface chip (the one in the corner of all VAXBI boards).
I see similar issues with an 8-bit CPU on a Unibus or Qbus.
Just something to keep in mind if you get high-byte/low-byte race
Ethan Dicks, A-333-S Current South Pole Weather at 5-Mar-2008 at 22:40 Z
South Pole Station
PSC 468 Box 400 Temp -57.5 F (-49.7 C) Windchill -91.9 F (-68.8 C)
APO AP 96598 Wind 12.1 kts Grid 64 Barometer 682.5 mb (10534 ft)
Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html