30 Aug
2012
30 Aug
'12
2:42 p.m.
Yeah, I kind of strayed into non-Z80 territory :-) It
was more a case of
pointing out that Torch made quite a vast range of stuff, but often the
Communicator and the twin-floppy units are the only things that people have
seen.
Somewhwere I have Torch lightpen for the Beeb. The lightpen itself is a
well-made anodised aluminuim thing, and I am pretty sure it was a
commercial device not made by Torch. It ends i a 5 pi nDIN plug with the
right pinput to fit a Gemini (Nascom++) video board.. The itenrfce is a
cheap plastc box that plugs into the 'aanlogue port' of the Beeb, from
which it draws 5V power. Of course the ligthpen output is fet into the
apporpirate pin of said port and thus to the 6845 in tge beeb. The
interface is essentially a switching regualtor to get the 12V needed fo
the lightpen from the 5V supply.
[Tatung Einstein]
Nice machines, from what I recall - it's a shame
they didn't catch on, but
I suppose they were just too late into the game.
It has some features in common with the BBC micro, but of course it's Z80
based. From what I remember :
The processor is a Z80A with 64K DRAM and a boot ROM which can be
swtiched in in place of 16K of said RAM. There's a fairly complete
machine code monitor (called 'MOS' (!)) in the ROM. It even has commands
to read and write disk sectors. One crazy feature, IIRC, is that this ROM
swithcing is controleld by a toggle flip-flip. A reference to a
particualr port address will swith hte ROM in if it's currently out and
vice versa. There's no way to force the ROM to be mapped in (other than a
hardware reset, whcih clears the flip-flop) or out. I seem ot remember
the Capp Lock LED is controlled in the same way which emans if you toggle
the FF once from your program (and change nothing else), the LED will be
in the wrong state until the next hardware reset.
The I/O chips include an AY-3-8910 sound chip. The poerts of this go to
the keyboard (scanned in software). A Z80A-PIO provides a Centroincs
pritner port and a user port. An 8251 provides an RS2232 port (with a
Z80A-CTC as the baud rate generator). The RS232 port is on a 5 pin
quincuncial DIN plug, but wired so that flipping it over does a
null-modem swap. The DSR and DTR signals are buffered ot RS23 levels and
end up on labelled solder pads on the PCB. An ADC0844 chip provided 4
analogue input channels, offocially for 2 joysticks. There are seaprate
DIN connectors for the 2 joysticks, not a common connector as on the Beeb
There is no cassette port, a floppy controller (WD1770) is standard. So
is a single 3" drive. There is space for another internal drive, and a
connecotr for exeenal drives. I think you can have up too 4 drives total.
It's a standard shugart bus, so you cna add 3.5" or 5.25" drives.
The video system uses the 50Hz version of the TMS9918 (I forget the
number) with 16K of video RAM There is a PAL wencoder and RF modualtor on
the board. There is also a montiutor csocket. Internal links select
between RGB and YUV on this connector, the latter being the factory
setting. This video system is what lets te machine down compared to the
BBC micro, there is no 80 column text mode. There was an 80 column
text-only add-on (it used a 6845 + RAM + cahracter genrator + glue
logic), but it's not at all easy to find. It is supported by the monitor
ROM, though.
-tony
cheers
Jules