Date : Sun, 20 May 2001 12:32:12 +0100
From : Mike Tomlinson <mike@...>
Subject: Re: Have I killed my Beeb?
In article <000901c0e10d$4e074e60$0c248ec6@...>, Adam
<alomac@...> writes
>It'll be a while before I can get photos, so I knocked up a couple of
>sketches at put them online at http://members.optusnet.com.au/~aloiacono/
>
>I'm not sure how clear they'll be though...
They're fine.
>From the Advanced user Guide: "In the lower right hand corner of the
keyboard PCB, there are two rows of eight holes. These are the keyboard
link options. The operation of these links is defined by a made or
unmade connection. The function of each link is as described under
OSBYTE 255. The diagram below illustrates the operation of these links.
If the user wishes to vary the settings fairly often, it is a good idea
to buy a standard 8 way SPST switch in a 16 pin DIL package, and solder
it onto the keyboard."
[Seen with the keyboard the right way up]
link 1 2 3 4 5 6 7 8
o o o o o o o o
o o o o o o o o
bit 7 6 5 4 3 2 1 0
bit 7 not used
bit 6 not used
bit 5 disc drive speed select
bit 4 disc drive speed select
bit 3 defines action of shift+break
bit 2 screen mode
bit 1 screen mode
bit 0 screen mode
Disc drive timing links [this will be for 8271 DFS]
link 3 link 4 step time settle time head load
1 1 4 16 0
1 0 6 16 0
0 1 6 50 32
0 0 [default] 24 20 64
>From your diagram, link 1/bit 7 is made. This is "not used" by the OS
so is redundant, unless it's been deliberately put there for other
software to read using osbyte 255.
Link 5/bit 3 reverses the action of shift-break, and as you were told by
someone else, holding down shift and pressing break re-reverses this
action, so that the machine starts up at a BASIC prompt. This is why
your typing in commands 'blind' (as you have no monitor) such as ctrl-G
and *MOTOR 0/1 work after you press shift-break. I assume you don't
have a disc drive connected; when you press break alone, the machine
hangs waiting for a disc drive to respond.
The factory default is to have all links open, so when you are able to
get a working display, you may want to open link 5 with a pair of wire
snips to stop the machine trying to boot on power up/break.
Links 3 and 4, set the speed of a disc drive. You have link 4/bit 4
made, which selects 6mS step time, 50mS settle, and 32 (mS? not sure)
head load. This is appropriate for a 5.25" half-height drive with a
head load solenoid.
Now for sketch 2...
This looks rather messy and I'm not sure what the intention is. Looks
like someone has tried to modify the startup options without
understanding how they are meant to work, or it does something clever I
don't understand (probably...)
As far as I can see, it simply duplicates the effect of making links 3
and 4 closed, so that you get the fastest disc drive stepping times
(step 4mS, settle 16mS, no head load, appropriate for a 5.25" half-
height drive with no head load solenoid - in other words, a drive where
the heads are in contact with the disc surface all the time. This is
most modern 5.25" and 3.5" drives.)
--
"Security-wise, NT is a server with a 'Kick me' sign taped to it."
- Peter Gutmann