Date   : Fri, 29 Sep 2000 06:44:11 +0100
From   : Mike Tomlinson <mike@...>
Subject: Re: 1770 disc interface

In article <39CFA3C6.C63EE023@...>, Philip Peake <philipp@...>
writes
>Hi all,
>
>Does anyone have a circuit diagram for the 1770 disc interface?

no, but have a look at the 1770 DFS upgrade kit fitting instructions at
the doc project:

http://members.magnet.at/marku/

there is also a '1770 DFS daughter board' in progress.  Not sure what
this is.

> Has anyone tried
>to build one (for the model B)?

no, but it should be do-able.  Wouldn't it be easier to find a
secondhand one?

>Can one do a straight swap WD1770PH for WD1772PH? 

yes, but the step rates are different - Acorn did at one point change
the 1770 chip on the BBC upgrade for a 1772. (The rom stayed the same.)
The jumper links on the keyboard changed and the fitting instructions
detailed what the links needed to be for both the 1770 and the 1772.  

Unfortunately, the copy of the instructions at the doc project don't
include the addendum sheet for the 1772 and I can't find a copy of it.
The default step rate for the 1770 was 6mS, on the 1772 with the default
liks it's 3mS, which is too fast for 5.25" drives.


> Also, does the 
>ADFS
>rom require the DFS rom to be present to work?

no

> And can the rom images at
>http://www.nvg.ntnu.no/bbc/roms/ be blown to PROM

yes

>As well as the 1770 module, the Acorn installation guide specifies that '2 off
>7438 Integrated Circuits' are required for the 14 pin DIL sockets at IC79 and
>IC80. Is the Texas Instruments SN7438N suitable for this?

yes.  Do not use the 74LS38.

-- 
Mike Tomlinson
mike@...