Date   : Sat, 29 Oct 2005 00:36:06 +0200 (BST)
From   : Johan Heuseveldt <johan@...>
Subject: Re: Dual Floppies On A Master

Hi Jonathan,

On Thu 20 Oct, Jonathan Graham Harston wrote:

[snip]

> The 1770 has no drive select lines. The drive must be selected
> with external hardware. The BBC and B+ only have two drive select
> lines, DS0 and DS1. The Master has three drive select lines, DS0,
> DS1 and DS2, allowing up to three drives to be selected. However,
> nothing in the DFS or ADFS drive access code ever selects the
> third drive. You would have to write your own disk system to
> access a drive with DS2. You may also have to set a link on the
> motherboard.

No links, but additional hardware, all marked as NF (not fitted):

  D1,D2,D3   1N4148
  R2         2K2
  Q1         BC239

D2,D3 forms a two input AND gate. R2 is the pull up resistor. D1 is
a safety measure for Q1. Q1 is both an inverter and an open colector
driver output (7438 alike). The AND combines the Motor On and DS2
signal, just as the two NANDS (1,2,3/4,5,6) of IC2 (7438) for DS0
and DS1 resp.

I have fitted these parts to one of the Masters and have played with
it for a while, using a 3.5" drive besides the two 5.25 ones.
As there is no support for it in the standard software, it means
writing NMI handlers yourself! In general it works, but I had a few
problems with the end result/phase of the 1770/2, not ending as
expected. It's all years back, and don't recall all the details. I
remember I need to write some background timings with the 100 Hz
service call, to time out a hanging 1770/2.

>From documentation, I think this was intended for a tape drive, that
uses the normal audio tapes, and connecting to the disc interface. In
another thread - about the MDFS tape drives, this type of drive was
mentioned briefly there.

I must have some official promotion documentation in which such a
tape drive was presented. No doubt the accompaning software deals
with the DS2 select signal, and a suite of managing software was
part of the bundle I reckon.

NB : this experiment needed a real Shugart drive. Indeed it was a
drive which has all the /four/ possibilities to set a jumper on one
of the /four/ available drive selects!

It's hard to find such a real Shugart compatible disc drive, as most
(all) of them are only IBM-PC compatible, meaning they are fixed to
drive-1 (out of 0-3), which should be clear from previous posts! :-)


greetings,
Johan

-- 
Johan Heuseveldt <johan@...              >
  aka  waarland

  The best place is a Riscy place
 
Life is anything that dies when you stomp on it.