Search found 1792 matches

by Kazzie
Sun Aug 23, 2020 6:58 pm
Forum: 32-bit acorn hardware
Topic: Restarting A3010
Replies: 3
Views: 341

Re: Restarting A3010

IanS wrote:
Sat Aug 22, 2020 6:06 pm
What's a CMPS?
That's what happens when the battery goes: bits start flipping one by one. :lol:
by Kazzie
Sun Aug 23, 2020 6:19 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23641

Re: 8271 disc controller craziness -- do not try this at home!

(I wish I had the time to get more involved with this analysis, it looks really fun!) Looking at the structure of the gates between the left and right sides of each of the two "ROM" areas in the bottom right, they're oriented the same way. So if the big ROM area has decoder circuitry on th...
by Kazzie
Sun Aug 23, 2020 8:19 am
Forum: 8-bit acorn hardware
Topic: Clock Failure
Replies: 24
Views: 1552

Re: Clock Failure

The bit I couldn't get to work was where it prints the "Clock failure" message, it's quite ingenious and took me a while to figure out how it works. It JSRs to the printing routine, and the string to be printed is in the code after the jump, and I eventually worked out from the Advanced U...
by Kazzie
Fri Aug 21, 2020 2:56 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23641

Re: 8271 disc controller craziness -- do not try this at home!

I'm a complete amateur at analysing thse things, but here we go... Working from the outside in, and looking at the pads. The pads on the left and right for power and ground are quite distinctive; they have large pads and two wires attached to each of them, and the traces taking the power supply thro...
by Kazzie
Thu Aug 20, 2020 7:20 pm
Forum: introduce yourself
Topic: Hello from Milton Keynes
Replies: 9
Views: 660

Re: Hello from Milton Keynes

BBCDave wrote:
Wed Aug 19, 2020 12:27 pm
Hello fellow Acorn enthusiasts
topcat96 wrote:
Wed Aug 19, 2020 3:21 pm
Howdy neighbour!

Am just a short hop down the A5 from you.
And I'm further along... but if you get to Holyhead you've gone too far! :lol:
by Kazzie
Mon Aug 17, 2020 12:38 pm
Forum: 8-bit acorn hardware
Topic: Safe archiving of 5.25" floppies?
Replies: 6
Views: 483

Re: Safe archiving of 5.25" floppies?

One problem you'd face is that the disc surfaces literally are floppy. What you describe is standard practice on hard drives, but while it's fairly practical to get a hard drive's head to float on a cushion of air above a flat rigid platter, I wouldn't expect it to be straight-forward to do on a flo...
by Kazzie
Sun Aug 16, 2020 7:03 pm
Forum: 32-bit acorn hardware
Topic: Acorn A3000 problem bad mouse pointer
Replies: 6
Views: 480

Re: Acorn A3000 problem bad mouse pointer

Are you up to reading through datasheets (specifically for the VIDC chip)? I had cursor corruption on a RiscPC, which turned out to be an early indicator of progressive failure on a buffer between the VIDC20 and the data bus. The key detail was that display data was coming directfrom the VRAM, but c...
by Kazzie
Sun Aug 16, 2020 1:17 pm
Forum: 32-bit acorn hardware
Topic: A7000 floppy drive not working
Replies: 2
Views: 283

Re: A7000 floppy drive not working

On the RiscPC circuit diagram, virtually every pin goes directly from the floppy connector to the 37C655, though some have pull-up resistors too. (Notable exceptions are ReadData and Index going via RC filters.) On that basis, you should be able to buzz out all but a handful of the pins from chip to...
by Kazzie
Sun Aug 16, 2020 7:13 am
Forum: 8-bit acorn hardware
Topic: VIDPROC V2 (pin 15) - please explain!
Replies: 33
Views: 1540

Re: VIDPROC V2 (pin 15) - please explain!

So, are we feeding in a higher Vreg, so that Vs is elevated relative to normal? In other words, VIDPROC is an overvoltaged ULA. Interesting. I'm not absolutely sure of that, given that the default setup was to have Vreg at Vcc. It is certainly above the minimum, though. Perhaps there was a tradeoff...
by Kazzie
Sat Aug 15, 2020 9:06 pm
Forum: 8-bit acorn hardware
Topic: VIDPROC V2 (pin 15) - please explain!
Replies: 33
Views: 1540

Re: VIDPROC V2 (pin 15) - please explain!

Now that I'm home, I can access my library, and my copy of Chris Smith's "The ZX Spectrum ULA". Early Spectrums also used the 5C000 series ULA, and he has a thorough explanation of the entire ULA family, as well as how it is used in the Spectrum. The ULAs are based on CML (current-mode log...
by Kazzie
Sat Aug 15, 2020 5:07 pm
Forum: 8-bit acorn hardware
Topic: VIDPROC V2 (pin 15) - please explain!
Replies: 33
Views: 1540

Re: VIDPROC V2 (pin 15) - please explain!

The 16MHz signal, as far as I can tell, goes nowhere, or somewhere (two LS393s), depending on the disk interface fitting and a jumper: BBC-Micro-16MHz.png S27 is only set to the 16MHz clock for using an 8 inch floppy drive, per section 4.6 of the Service Manual. Given the responses to a thread last...
by Kazzie
Fri Aug 14, 2020 2:58 pm
Forum: for sale / freebies
Topic: For sale: Master and lots of other bits
Replies: 20
Views: 2018

Re: For sale: Master and lots of other bits

I'm also interested in the BBC Master if you're prepared to ship to Guernsey (it's normally only a few quid more which I'd cover). I can't PM you yet as I just joined the site. Are you able to PM me first so I can reply? You wouldn't be able to reply via PM yet either (unless you use the "cont...
by Kazzie
Thu Aug 13, 2020 2:06 pm
Forum: 8-bit acorn hardware
Topic: Unknown board connected to 6845 CRT controller
Replies: 24
Views: 1275

Re: Unknown board connected to 6845 CRT controller

Do you think it's something that I should clean/tidy up and keep connected, or should I just document how it was connected and restore the Model B to how it should be? I'd suggest trying to work out exactly what it is and does before removing it. If I get a chance this evening, I'll have a go at re...
by Kazzie
Thu Aug 13, 2020 10:27 am
Forum: 8-bit acorn hardware
Topic: Unknown board connected to 6845 CRT controller
Replies: 24
Views: 1275

Re: Unknown board connected to 6845 CRT controller

The 16MHz crystal is the Beeb's master clock crystal, dismounted from the board: the blue and yellow wires can be seen connecting it to the X1 position on the board. The Light Pen Strobe LPSTB on pin 3 is an input that has a pull-up resistor fitted on the Beeb. The only other connection of LPSTB is ...
by Kazzie
Thu Aug 13, 2020 6:33 am
Forum: 32-bit acorn software: other
Topic: Bug in RISC OS Time/Date?
Replies: 7
Views: 670

Re: Bug in RISC OS Time/Date?

Guessing here: Might it be related to the fact that it's currently BST?
by Kazzie
Wed Aug 12, 2020 2:08 pm
Forum: for sale / freebies
Topic: Acorn Special Needs Keyguards
Replies: 1
Views: 292

Re: Acorn Special Needs Keyguards

Very interesting.

For the benefit of anyone who hasn't encountered keyguards before, this page gives some explanation as to their use.
by Kazzie
Wed Aug 12, 2020 1:45 pm
Forum: 8-bit acorn hardware
Topic: Refurbishing a Torch Z80 Disc Pack
Replies: 13
Views: 741

Re: Refurbishing a Torch Z80 Disc Pack

I have a vague memory that 79xx regulators have a non-ground pin connected to their backplate, and thus they need to be insulated. At least, that's what I recall from looking at a Dragon32 PSU, where some regulators were electrically connected to the heatsink, and others weren't.
by Kazzie
Wed Aug 12, 2020 1:42 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 5792

Re: Silent, nothing visible

The blue trace is Pin37, the yellow trace Pin39. The input and output clocks for the 6502? That's odd, then. The photo you posted has the blue trace at a scale of 20V per division (presumably with the probe set to 10x), and a peak-to-peak measurement of roughly 4V, which is perfectly reasonable. Th...
by Kazzie
Wed Aug 12, 2020 12:46 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 5792

Re: Silent, nothing visible

What did you make of the little vid with the trace moving up and down like that? I hadn't looked at that (my phone's browser doesn't download forum attachments properly, I have to do some workarounds). If I'm reading your annotations correctly, in the video the blue trace is pin 35, at a vertical s...
by Kazzie
Wed Aug 12, 2020 12:26 pm
Forum: 32-bit acorn hardware
Topic: My first proper post - Acorn RiscPC600 - Battery damage and possible VIDC issues
Replies: 12
Views: 780

Re: My first proper post - Acorn RiscPC600 - Battery damage and possible VIDC issues

Glad you got something sorted. 8)

Was it the damaged board you passed on, or the working system? Best not to throw out the old board, in case someone else can repair it or use it for parts - they're not making any new ones!
by Kazzie
Wed Aug 12, 2020 12:19 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 5792

Re: Silent, nothing visible

Have a look though the rest of the pins, and tell us what you see.
by Kazzie
Wed Aug 12, 2020 11:02 am
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 5792

Re: Silent, nothing visible

Apologies: I wrote two descriptions for pin 20, and none for pin 21. Pin 20 is address line A11, pin 21 is ground. #-o

I'll correct the post above for any future readers.
by Kazzie
Wed Aug 12, 2020 7:13 am
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 5792

Re: Silent, nothing visible

I can't give an expected values list that's quite as explicit as the 555 reset timer, because the 6502 is (obviously) a much more complicated chip that does more than make a reset pulse. I can give a rundown of what to expect on a 6502 that's in a good, healthy board. Let's work our way down from pi...
by Kazzie
Tue Aug 11, 2020 6:31 pm
Forum: 8-bit acorn hardware
Topic: Clearing EPROMS/EEPROMS
Replies: 59
Views: 2460

Re: Clearing EPROMS/EEPROMS

It's not directly relevant to your EPROM issues, just explaining why a small bit of code was off on its own: it needs to be there because that's where the CPU will look for it. Now, that makes sense!! IRQ = Interrupt Request (got that) NMI = ??? Reset = Yeah got that one. What's NMI? A non-maskable...
by Kazzie
Tue Aug 11, 2020 6:27 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 5792

Re: Silent, nothing visible

Don't worry about going back to the minimal configuration; you've establised that removing them didn't resolve the problem, and Tricky's ROM needs the VIA present to do anything useful, anyway. Just to check: when you say nothing's working, does that include no flashing LEDs or cassette relay clicks...
by Kazzie
Tue Aug 11, 2020 6:18 pm
Forum: 8-bit acorn hardware
Topic: Clearing EPROMS/EEPROMS
Replies: 59
Views: 2460

Re: Clearing EPROMS/EEPROMS

These six bytes are vector addresses for the code the 6502 will use when it gets an IRQ, NMI, or RESET input: 0xCAE3 and 0xC000. When placed in the OS socket, the six bytes end up at the very top of the memory map, 0xFFFA - 0xFFFF, rather than 0x3FFA - 0x3FFF in your programmer. Charlie Brown momen...
by Kazzie
Tue Aug 11, 2020 5:35 pm
Forum: 8-bit acorn hardware
Topic: Clearing EPROMS/EEPROMS
Replies: 59
Views: 2460

Re: Clearing EPROMS/EEPROMS

So, looking at Tricky's ROM image the end of the file appears to be padded with 00 except the last six (addresses) ending at 0x3FF0 which are E3 CA 00 C0 E3 CA These six bytes are vector addresses for the code the 6502 will use when it gets an IRQ, NMI, or RESET input: 0xCAE3 and 0xC000. When place...
by Kazzie
Tue Aug 11, 2020 5:17 pm
Forum: 32-bit acorn hardware
Topic: CF on RiscPC IDE/ADFS - bizarre success
Replies: 4
Views: 416

Re: CF on RiscPC IDE/ADFS - bizarre success

How utterly bizzare!

When you tried versions 2.46 and 2.48, were they running locally or over ShareFS?
by Kazzie
Tue Aug 11, 2020 5:10 pm
Forum: 32-bit acorn hardware
Topic: Repair thread: RiscPC 600
Replies: 27
Views: 1980

Re: Repair thread: RiscPC 600

In my case, there was definitely an element of distraction from kids: after wicking away all that I could of the solder I'd snipped the legs on one side of the chip, but forgotten to cut the other side before trying to lift the chip. :oops: A through-hole chip would have bent at the legs, but I'm wo...
by Kazzie
Tue Aug 11, 2020 7:46 am
Forum: 8-bit acorn hardware
Topic: Kenda "The Professional" DMFS
Replies: 83
Views: 4029

Re: Kenda "The Professional" DMFS

Most of the time, if you were using a 24-pin EPROM in a 28-pin socket, you'd mount it at the base, to align the data and address pins etc. That arrangement, with the transition socket mounted at the top, leaves three data pins and ground unconnected. The data bus is also accessible from the 8271 soc...

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