Search found 7990 matches

by hoglet
Mon Apr 22, 2019 1:42 pm
Forum: acorn atom and system
Topic: Atom Noise Killer @ 2MHz
Replies: 28
Views: 519

Re: Atom Noise Killer @ 2MHz

Hi Phill, First half of the video is displaying menu with the sta #8000 loop. I then hit break and just boot the mmc, which displays the standard games collection menu, which shouldn't be accessing the video RAM, and I'm still getting the same noise so I'm at a loss to see where it is coming from :(...
by hoglet
Sat Apr 20, 2019 6:09 pm
Forum: acorn atom and system
Topic: Atom Noise Killer @ 2MHz
Replies: 28
Views: 519

Re: Atom Noise Killer @ 2MHz

I rather suspect it's noise that's getting onto the Y line, as it only appears in areas of the screen where the Y signal is used. If you change the test program to: [ LDA #8000 JMP #9C00 ] do you still get noise? I'm wondering if during CPU writes there is a brief bus conflict, where momentarily bo...
by hoglet
Sat Apr 20, 2019 8:34 am
Forum: hardware
Topic: Electron Plus 1 ROM emulation and SD interface using an STM32F4
Replies: 9
Views: 416

Re: Electron Plus 1 ROM emulation and SD interface using an STM32F4

I've made some updates. I haven't implemented interrupts or a FAT32 driver as yet, but I've added in 4 sideways RAM slots (4, 5, 6 and 7) alongside the 4 ROM slots that were already implemented (12, 13, 14 and 15). This way I can load the Electron Sideways RAM version of MMFS (ESWMMFS) into slot 4 ...
by hoglet
Sat Apr 20, 2019 7:14 am
Forum: hardware
Topic: T65 core
Replies: 2
Views: 141

Re: T65 core

I've been using the T65 core for some of my recent testing and I think I've found some bugs but I'm not sure that I'm using the latest. The one I'm using is from https://github.com/MiSTer-devel/VIC20_MiSTer/blob/master/t65/T65.vhd version 313. That's the most recent version I could find as well. I ...
by hoglet
Fri Apr 19, 2019 6:32 am
Forum: programming
Topic: What PRNG algorithm's do BBC BASIC's RND functions use
Replies: 22
Views: 361

Re: What PRNG algorithm's do BBC BASIC's RND functions use

This is an illustration of the Beeb's PRBS:
PRBS.PNG
( from Acorn User August 1984)

It should make understanding the various implementations a bit easier.

Dave
by hoglet
Thu Apr 18, 2019 6:28 pm
Forum: programming
Topic: What PRNG algorithm's do BBC BASIC's RND functions use
Replies: 22
Views: 361

Re: What PRNG algorithm's do BBC BASIC's RND functions use

It seems:

- Basic 2 runs the shift register one bit at a time (hence 32 iterations)

- Basic 4.00 runs it one bytes at a time (hence the 4 iterations)

- So Basic 4.23 must run it two bytes at a time (hence only 2 iterations)

All very neat!

Dave
by hoglet
Thu Apr 18, 2019 6:25 pm
Forum: programming
Topic: What PRNG algorithm's do BBC BASIC's RND functions use
Replies: 22
Views: 361

Re: What PRNG algorithm's do BBC BASIC's RND functions use

Here's the Basic 2 code, for reference: .LAF87 LDY #&20 .LAF89 LDA &0F LSR A LSR A LSR A EOR &11 ROR A ROL &0D ROL &0E ROL &0F ROL &10 ROL &11 DEY BNE LAF89 RTS And the Acorn Atom code is very identical, except using different zero page locations. C986 A0 20 LDY #&20 C988 A5 0A LDA &0A C98A 4A LSR A...
by hoglet
Thu Apr 18, 2019 4:57 pm
Forum: programming
Topic: What PRNG algorithm's do BBC BASIC's RND functions use
Replies: 22
Views: 361

Re: What PRNG algorithm's do BBC BASIC's RND functions use

Is it possible to tell, with the different versions of Basic, whether it's just the implementation that has improved, or whether they also switched to a new generate polynomial?
by hoglet
Thu Apr 18, 2019 10:07 am
Forum: acorn atom and system
Topic: Atom Noise Killer @ 2MHz
Replies: 28
Views: 519

Re: Atom Noise Killer @ 2MHz

Prime wrote:
Thu Apr 18, 2019 9:36 am
And I'm sure you meant try increasing R by ~50% to 150R......
Sorry, I ended up changing to using 100pF and 220R (rather than 220pF and 100R). I didn't update the earlier schematic.

Anyway, I'm expecting to have to fiddle with the values a bit more.

Dave
by hoglet
Thu Apr 18, 2019 8:24 am
Forum: acorn atom and system
Topic: Atom Video to HDMI Adapter
Replies: 34
Views: 577

Re: Atom Video to HDMI Adapter

Hi Hoglet & everyone, I would be very interested in obtaining an HDMI & video ram board - these look really good and it's about time I boosted my Atom (currently just has Atommc and an analogue colour board) - are there any spare? There will be plenty of spare boards and it's be easy to order more ...
by hoglet
Thu Apr 18, 2019 6:38 am
Forum: acorn atom and system
Topic: Atom Noise Killer @ 2MHz
Replies: 28
Views: 519

Re: Atom Noise Killer @ 2MHz

The noise killer circuit however seems just on the edge (well in my lashup anyway, which was done on a piece of tripad). There are two distinct timing paths that seem to matter in the noise killer: (1) - the latch must freeze before the video data on the RAM output becomes unstable (2) - the latch ...
by hoglet
Wed Apr 17, 2019 9:46 pm
Forum: acorn atom and system
Topic: Atom Video to HDMI Adapter
Replies: 34
Views: 577

Re: Atom Video to HDMI Adapter

roland wrote:
Wed Apr 17, 2019 9:39 pm
Hmmm ... I'm a bit to enthusiastic :lol: I'll wait until you have tested the boards.
On the other hand, it costs almost nothing to add 5 or 10 boards onto an existing order.
by hoglet
Wed Apr 17, 2019 9:32 pm
Forum: acorn atom and system
Topic: Atom Video to HDMI Adapter
Replies: 34
Views: 577

Re: Atom Video to HDMI Adapter

Hi Roland, If there is no more further demand for it I'll order five boards this weekend for the Dutch audience. I sent these three boards to JLCPCB yesterday: pcb1.png pcb2.png pcb3.png There are all completely untested, so caveat emptor! They are already 62% of the way through the manufacturing pr...
by hoglet
Wed Apr 17, 2019 3:28 pm
Forum: hardware
Topic: Raspberry Pi to 1MHz bus interface
Replies: 64
Views: 2421

Re: Raspberry Pi to 1MHz bus interface

Here's a couple of photos of the actual interface.
IMG_1629.JPG
IMG_1630.JPG
No active components, just 1N4148 diodes and 100R resistors.

Dave
by hoglet
Tue Apr 16, 2019 10:27 am
Forum: acorn atom and system
Topic: Atom Noise Killer @ 2MHz
Replies: 28
Views: 519

Re: Atom Noise Killer @ 2MHz

I wonder if I can do something similar with the spare gates on the 74HCT00 and 74HCT14? It turns out I do have enough spare gates of the right type to generate a shaped write pulse of ~60ns duration. I've just tested the following circuit on the breakboard: Selection_022.png The new write pulse loo...
by hoglet
Tue Apr 16, 2019 9:49 am
Forum: acorn atom and system
Topic: Atom Noise Killer @ 2MHz
Replies: 28
Views: 519

Re: Atom Noise Killer @ 2MHz

I've also run across a problem with some combinations of faster RAM / 6847, where the RAM would actually become corrupt which I suspected was the address lines from the 6847 changing the values on the RAM's address lines befor the /WE had gone completely high leading to data being written to the wr...
by hoglet
Tue Apr 16, 2019 7:26 am
Forum: acorn atom and system
Topic: ICET-6809
Replies: 15
Views: 585

Re: ICET-6809

I tried your updates to the timing, still doesn't seem to improve things. OK, that's a shame. Once I get through the backlog of PCB designs, I'll have another think. Now comes the odd part, if I thin use the test command to test all the ram so : TEST 0000 7FFF all the tests pass, I've tried doing i...
by hoglet
Mon Apr 15, 2019 8:45 pm
Forum: acorn atom and system
Topic: Atom Noise Killer @ 2MHz
Replies: 28
Views: 519

Re: Atom Noise Killer @ 2MHz

A 5.10c colour board and noise killer .. I do see some sparklies but I think thats from the Atom rgbtohdmi, not the noise killer when the atoms connected to a tv via scart Phill's larger sized colour boards all make use of the 8304 on the Atom's board, which buys some extra timing margin. I wouldn'...
by hoglet
Mon Apr 15, 2019 8:37 pm
Forum: acorn atom and system
Topic: Atom Noise Killer @ 2MHz
Replies: 28
Views: 519

Re: Atom Noise Killer @ 2MHz

IIRC there was also a difference in timing for the 123 types according to the specs. Yes indeed there is, and that need's to be taken account of by using a different capacitor value: - 74LS123 + R=8K2 + C=150pF (in the original Alan Knowles article) - 74HC/74HCT123 + R=8K2 + C=68pF (on Phil''s boar...
by hoglet
Mon Apr 15, 2019 6:43 pm
Forum: acorn atom and system
Topic: Atom Noise Killer @ 2MHz
Replies: 28
Views: 519

Re: Atom Noise Killer @ 2MHz

(Nudge, as parts 2 and 3 updated)
by hoglet
Mon Apr 15, 2019 2:38 pm
Forum: acorn atom and system
Topic: Atom Noise Killer @ 2MHz
Replies: 28
Views: 519

Re: Atom Noise Killer @ 2MHz

Why was there a third post reserved? For an epilogue of course. :D In the course of these experiments, I've discovered some interesting facts about the original noise killer. At least on my board, the original noise killer design is only just working. Works most of the time, but I occasionally see s...
by hoglet
Mon Apr 15, 2019 2:38 pm
Forum: acorn atom and system
Topic: Atom Noise Killer @ 2MHz
Replies: 28
Views: 519

Re: Atom Noise Killer @ 2MHz

Let the story resume... To have a chance of working correctly at 2MHz and 4MHz, two things have to change: (1) The screen memory should be faster (2) The length of the latch LOAD pulse needs to vary, depending on the clock speed. It's easy/cheap to get hold of 55ns RAM (Phill uses these on his video...
by hoglet
Mon Apr 15, 2019 2:38 pm
Forum: acorn atom and system
Topic: Atom Noise Killer @ 2MHz
Replies: 28
Views: 519

Atom Noise Killer @ 2MHz

Hi all, I've been wondering since yesterday if it's possible to somehow tweak the screen noise killer to work at 2MHz (and beyond). So I've spent this morning doing some "Evil Mad Scientist" type experiments. :shock: Now it's time to present the results... But first, let's recap a bit about the caus...
by hoglet
Mon Apr 15, 2019 5:25 am
Forum: acorn atom and system
Topic: Atom Video to HDMI Adapter
Replies: 34
Views: 577

Re: Atom Video to HDMI Adapter

Hi Chris, Can you me down for an Atom Video to HDMI Adapter please? Just to re-iterate what I said in the first post, I'm happy to make bare PCBs available, but I'm not currently planning to build and sell completed units. I do enjoy assembling the first unit (because of the anticipation of will it ...
by hoglet
Sun Apr 14, 2019 7:37 pm
Forum: other vintage computer hardware, software and games
Topic: Those Spectrum nerds, eh?
Replies: 26
Views: 480

Re: Those Spectrum nerds, eh?

Though more seriously, did many enthusiasts use their BBCs at school for things like Morse code and other technical exercises, for the sake of the exercise? Yes, indeed they did, myself included. :D I spent ages trying to write a morse code decoding program for the Acorn Atom, without much success,...
by hoglet
Sun Apr 14, 2019 7:32 pm
Forum: for sale / freebies
Topic: Electron MicroSD Card Interfaces (SOLD OUT)
Replies: 105
Views: 3462

Re: Electron MicroSD Card Interfaces (SOLD OUT)

I have a big development board that supports sideways RAM, ROM (flash & eproms) with very flexible mapping. I did try SW MMFS in a split RAM/ROM bank, but was never able to get it working. At the moment the best way forward I can see is to do a board with some SRAM and standard MMFS in flash, and s...
by hoglet
Sun Apr 14, 2019 6:01 pm
Forum: acorn atom and system
Topic: Atom Video to HDMI Adapter
Replies: 34
Views: 577

Re: Atom Video to HDMI Adapter

Hi all, I've knocked up a quick "8K Video RAM and Noise Killer" board, as a companion to the HDMI Video adapter. NoiseKiller1.png NoiseKiller2.png This is pretty close to what Phill used on his Mk 3.5 Video Board. The current schematic is here: https://github.com/hoglet67/AtomRamAndNoiseKiller/blob/...
by hoglet
Sun Apr 14, 2019 1:17 pm
Forum: acorn atom and system
Topic: Atom 2k18 ?
Replies: 204
Views: 6241

Re: Atom 2k18 ?

Can you let me have some gerber files? They are much easier to review.

Where are you with design rule checks in the PCB layout program? All passing?
by hoglet
Sun Apr 14, 2019 1:14 pm
Forum: hardware
Topic: MMFS Development and Support
Replies: 770
Views: 52843

Re: MMFS Development and Support

Does such a version exist? No, but it's easy to add. I've done a test build here: mmfs_test.zip The build you need is MMFS3.rom (which uses &FEA0 as the VIA address). Please give this a try and see if it works. Unfortunately, with these extra builds, some of the disks images are overflowing during ...
by hoglet
Sun Apr 14, 2019 9:37 am
Forum: acorn atom and system
Topic: Atom 2k18 ?
Replies: 204
Views: 6241

Re: Atom 2k18 ?

Thanks Dave. Yes, I have one of these as well. I think I'm going to settle with my original measurements (between the closest pins) of: - horizontally offset by 0.175" - vertically offset by 0.25" I'm using 1mm holes, so there is a bit of play when soldering the headers in. What I usually do is to f...