More Acorn finds + Numonics graphics tablet

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Thu Jul 24 18:27:00 2003

> Master 128 with a Cox 630B genlock card
Is that 'Michael Cox Electronics'? I've come across said company for
video-related stuff (PAL encoders/decoders) before.

> Acorn RGB monitor w/SCART connection

Almost certainly a badged Philips unit. It's analogue RGB only (unless
you get the service manual for the Philips version and solder in the
components for the PAL decoder, and then align the darn thin). The pinout
is standard SCART, with the sync going in on the composite video input
pin (as you'd expect if you've worked with SCART before).

> Three of the BBC B machines have an IC/module plugged into one of the ROM
> sockets with a label saying "RAM". The modules are twice the height of a normal
> IC and have a red and black wire coming out of them. The red wire is soldered
> to the system board; the black wire has an IC leg clip at the end of it. Any
> ideas what these are?

Sideways RAM. These are RAM modules (normally 16K -- you may find the
module contains a pair of piggybacked 6264 chips) that pretend to be
sideways ROMs to the system most of the time. The 'official' reason for
wanting one was to be able to develop sideways ROM code easily. The real
reasonfor having one was that you could copy ROM images to disk from
other people's machines, then load them into the RAM module and pretend
to have that ROM. This is commonly called theft, of course!

>
> What does that Watford DDB3 module do?

Well, it plugs into the 8271 (disk cotnroller chip) socket. So it's
probably a 1770 board. Such boards were designed when the 8271 became
almost impossible to obtain, and also allowed the use of double-density
(MFM) recording. You need thr correct DFS ROM for them, and some of the
lesser ones fail on copy protection schemes that try to access the 8271
driectly. Better DFSes (including Acorn's IIRC) attempt to translate
accesses to the 8271 (at least if you use the appropriate OSBYTE call,
which you should do to make the program second-processor compliant) into
the equivalent operation on the 1770.

-tony
Received on Thu Jul 24 2003 - 18:27:00 BST