[BBC-Micro] TUBE chip, accessing 'Parasite' side
johan at waarland.demon.nl
Mon Mar 3 22:48:09 GMT 2008
On Mon 03 Mar, Pete Turnbull wrote:
> On 03/03/2008 17:14, Johan Heuseveldt wrote:
> > I refound the schematics for the internal CoPro 80186, but couldn't find
> > anything else.
> Try http://www.bbcdocs.com/ and follow the link for Hardware. The
> diagrams for three coprocessors including the external 6502 are near the
> bottom of the page.
I've never found that before! And I looked so much there.
I have great difficulties in accessing pages, as incoming pages freezes
very easily, although there is a significant improvement after Demon
went to XS4ALL (without changing the email address)
Direct links to somewhere deep into a site, mostly gives a direct result.
> With my own 6502 external 2ndProcessor, I've investigated a
> > few things. It appears that the power connections to the TUBE chip are more
> > advanced than I first assumed, which makes sense as this chip - besides the
> > logical model for the TUBE software protocols - must also handle two
> > independant power connections, and some safety precautions are apperently
> > necessary!
> I expect you're looking at the circuitry around LK1 and LK3. It also
> has provision for power to be taken from the cheese wedge PSU or
> alternatively from the Tube.
Actually, when powered from the wedge PSU, there's still a connection to the
TUBE chip - pin 4 - powered from the flat cable, from LK3 indeed, which is
hard wired as such (a-b). Normal VCC power - the external wedge PSU - is
wired to pin 2. GND is at pins 1 and 5.
The a-c connection would connect to the main PSU, which is the external wedge
PSU. With LK1, the +5V from the flatcable (coming from the Beeb of course)
can be connected to the boards main VCC line.
A third connection at the TUBE chip - pin 3 - is a special case, having a 12
ohms 1 Watt resistor to the main VCC (from the wedge PSU). The Z80 board has
even an extra coil in serial with that. I suppose this is vital when used
with two PSUs, as either one can be switched off!
The schematics of the internal 80186, shows pins 2 and 4 connected and wired
to the single internal VCC, leaving the special one at pin 3 open.
> > The '004' document for the TUBE doesn't say anything how fast the parasite
> > side can/may be accessed. Even an pin description is without pin numbers.
> No, sadly it only says how quickly the parasite needs to respond to keep
> up, ie the lower limit -- not what the upper limit is. The Arm Eval or
> 32016 circuits might give a clue; I've not looked. You won't have a
> problem with a 68B09, though (I know because (a) it's been done and (b)
> that's about the same bus speed as the corresponding 2MHz 6502A or a
> 4MHz Z80A).
Indeed my assumption is I'll get away with no slow down used.
The notREAD and notWRITE signals are created by synchronizing the RnW with
the E clock, which can be driven constantly, just as in the Beeb, as the TUBE
chip has a separate notCS input. See 8271 and 7002 (B, B+)
Some first observations from the 3 MHz 6502 external board shows the nRD and
nWR coming from a 74 FlipFlop, so I was suspecting a slow down there. The
internal 65C102 CoPro in the Master is even at 4 MHz.
But perhaps I would be able to access the schematics mentioned above.
If so, it could also give me the value for the timing C for the RESET
signal from the 74LS122N, which is unmarked, but looks the same as all the
Thanks for the info. After finishing this, I'll go there...
Johan Heuseveldt <johan at waarland.demon.nl>
The best place is a Riscy place
Acid consumes 47 times its weight in excess reality.
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