This Weekend's Finds

From: Philip.Belben_at_powertech.co.uk <(Philip.Belben_at_powertech.co.uk)>
Date: Mon Aug 18 10:28:17 1997

> > I bought: A TI-99/4A (Not as lucky as Roger M - I paid L12 with no
> > joysticks, manuals or cartridges, but I did get the UHF thingy)
>
> Nice!!!....

Yes, my first TI computer (I have a broken calculator and a Silent 700
or two...)

> > But the real find: A British Telecom Microscribe for L1
>
> Very nice...
>
> > This object is a solidly built sub-notebook (about 7 in square by 1
> > thick) with a dinky keyboard and a palmtop-sized LCD. It has 32K of RAM
> > and 16K of ROM, and the processor is an Hitachi HD63A03XP single chip
> > microcomputer.
>
> Is that the only processor? It sounds as though it might be distantly
> related to a Thorn-EMI machine called a Liberator which had a 63-something
> for I/O and a Z80 running a CP/M like OS (or at least, that what I think
> is inside it - the ROM is (C) Digital Research, and running strings on a
> ROM image turns up some interesting stuff)

'fraid so. Indeed, it is the only chip with >28 pins (apart from the
flatpacks on the back of the LCD). IC master, just to be perverse,
gives various 6301 and 6305 variants in that series, but nothing of 6303
flavour.

> Not so. A lot of machines use the NiCd as the smoothing component. HP
> certainly did in just about all of their more recent NiCd calculators (the
> ones that use the 8V 50mA AC charger).

Interesting. I haven't found where the battery gets in, but the input
stage is something like:

                Diode
Ring --+--/\/\/-|>|-+-----+
       | 56R | \
       | |C / 82R
       | |/ \
       +-/\/\/-+--| NPN /
               | |\ |
               _ |E |
Tip--+ Zener A +-----+--- +5V? to rest of machine (??)
     | |
    GND GND

I would guess the battery could well do any smoothing downstream of the
regulator, but I'd still like to see some upstream of it!

If the machine draws 60mA, minimum voltage at input is around 9V,
maximum around 13V, so I suppose I could try 10V and see what happens...

> Some, like the Epson HX20 even used the fact that the voltage across the
> NiCd would go above 5V to limit the supply voltage to the chips. The
       ^^^^^
I take it you mean wouldn't

> If you have an adjustable PSU, apply about 5V, and then crank it up
> towards 9V (I'd guess that's what it takes), monitor the 5V line and stop
> if it rises above (say) 5.5V. See what current flows - it should be
> arround 50mA.

Worth a try.

Philip.
Received on Mon Aug 18 1997 - 10:28:17 BST