stardot.org.uk

Alkaline batteries in a holder: https://cpc.farnell.com/pro-power/pp002109/battery-box-2x-aa-waterproof-wired/dp/BT06560 (Waterproof/sealed case, not suitable for rechargeables) Wire a 1N4148 diode in series with the positive lead to block charging voltage (and a 220R resistor if you want to go ful...

For sure the ULA was way to ambitious for its time. It killed the potential sales by missing Christmas. A less ambitious approach to reducing the chip count should have been used. If just missing Christmas could hole its chances so fatally, surely that's a clue to the white elephant the machine mus...

Supposing the Elk had contended Video Access (like Spectrum) to simply ULA and reduce RAM speed requirements (ie 2Mhz ram rather 4Mhz for 2Mhz processor): could the slowinmg down effect be mitigated a bit by subdividing the Shared area into blocks so that only the sub-block currently read by ULA wo...

Superb job Ken, looks excellent =D> 8) For a complex board, it not unusual for one, two or three minor errors to creep in. I hadn't noticed that: have you "stolen" one of the three sets of PSU power connectors from the main board, and are sending the power through to the main board via the CPU socke...

I keep meaning to make a spoken starup "sound" if you have a speech processor, but never seem to get around to it. Not “Good evening, Dave. Everything’s running smoothly” :shock: :lol: HAL2000 https://2001archive.org/sounds/ Couldn’t find a quote where HAL says “Sorry Dave, I’ve blown up my capacit...

What size holes did you use for the battery pads? Now rather than fitting a battery or a cell directly to a PCB, going forward, I intend to use through terminal hole pins, so that it makes it easier to change in the future.

Mark

They look good

Only one problem...

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I can’t see the pads for the flux capacitor

Good luck with testing

Mark

For a U.K. spec BBC B, yes, the far right socket is the highest priority.

On third party expansion boards, normally the one labelled 15 is the highest (or 14 if 15 is RAM).

Mark

There is not much documentation on either the US or the German versions :( The principles of fault finding remain the same however. And the circuitry is believed to be very similar. But chip IDs are different and where a chip provides more than one logic gate/function, pin numbers may be different a...

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Mark

No, but keep in mind that the forum compresses large image files, so I blame that rather than my eyes :lol: It’s always a good idea to clean a PCB with IPA and a toothbrush (but not the one you use to clean your teeth!) after soldering work. As the sticky flux that is left behind can hold all manner...

If you leave the 8255 out of it’s socket, and leave the EPROM out of the Beeb’s ROM socket, you can use BASIC along with a logic probe, ‘scope or even just a 470 ohm resistor and red LED to test if the 6522 VIA I/O Pins are working. It’s a bit hard to easily test the DRAM on the Torch Z80 board, due...

Oh, that reminds me...


Mark

As there is no address decoding on this board, the 74LS245’s direction pin (pin 1) would normally be controlled by the external device. As this control line should only switch the 74LS245 to drive the CPU data lines when the CPU address bus lines are set to within the required address range, the CPU...

Looks like that board is buffering all the address and data lines.

Mark

@Dave - so would that be RAMdom failures

Mark

A Master with the appropriate expansions can now emulate more computers than any other eight bit home computer. Who would have predicted that!

Mark

Don’t know, but quite some years ago two ZX81’s were linked, one generated the display while the second one ran the users program, thereby speeding up execution.

Before recent times, second processors were expensive and hard to find, so this may have been the limiting factor.

Mark

Some have a 15 way D connector that has solder tabs to secure it to the PCB rather than screws or machine screws/bolts and nuts.

Mark

So the ADC chip is fitted

Mark

It may help if you have a look at the underside/solder side. Look at the component and chip pads. Flow soldered pads are normally clean and very consistent. If you see any flux (black/brown/tan coloured deposits) around solder joints / pads, or the solder joints are not consistent (varying amounts o...

Noted . . . I know the answer - but just to check: Can FPGAs be "locked" ? 8-[ :- Depends on the part... it's a read the datasheet(s) job for each one. Is it a type with internal configuration Flash/EEPROM or a type that reads it’s configuration from an external Flash/EEPROM chip? Mark

It was terrible! 200 to 600 cycles, depending on bus width. Maybe, but that did not stop computers based on them from having disk drives for example. The bottom of the range Atari STFM 520 can, with a relatively simple internal hardware add-on, can use HD floppy disks and drives (reading and writin...

Don't forget that the BBC/Proton had a 6502 running twice as fast as that in the System and Atom. So in this alternate reality, Acorn would already have made a 4MHz Z80 system and would be looking to double the performance... and the Z80 didn't have the headroom for that, I think. Perhaps Acorn wou...

There are only five versions of the BBC A/B main board/motherboard (the very rare issue 1, issue 2, issue 3, issue 4 and issue 7). The issue 4 and issue 7 are the most common. There are (as far as I am aware) two versions of the BBC Master main board/motherboard. I think there is just one version of...

http://8bs.com/insides.htm
http://chrisacorns.computinghistory.org.uk

Does that help?

Mark

< like >

Mark

If Acorn had used a Z80, then I would have expected them to have designed the system to “boot” to BASIC in ROM. Just like the 6502 BBC Micro does. If the BBC Micro had been designed with a Z80, I very much doubt that Acorn would have designed and sold a 6502 second processor. More likely that they w...

MartinB wrote: ↑

Tue Feb 12, 2019 7:48 pm

The lids can be screwed on....?!

Not when you (meaning me) have, err, safety stored the screws somewhere that you can’t currently remember...

Mark

The recent discussion kicked off by Sunrise has made me decide I need to take a break from contributing. I first wish to thank you for all your hard work. The site is excellent and being a major contributor, a lot of that is down to you. So well done =D> =D> =D> Secondly, I think you are misinterpr...