BBC Model B implementatation for myStorm BlackIce

Speculatrix 2017-12-30 10:50:36 UTC #81

Care to share a schematic? I've just come back to this after a break and now find that none of my keyboards work. (And I'm damn sure that several did before, via a PS/2-USB adapter).

hoglet 2017-12-30 12:41:10 UTC #82

A schematic of what?

Speculatrix 2017-12-30 13:45:07 UTC #83

I was replying to Emuboy who mentioned he'd built a PS/2 adapter with level shifter. I've been having trouble with keyboards today - I tried about six without luck. Then I put the scope on the board and found that at least one of my keyboards was, in fact, sending codes okay. Weirdly, when I plugged into a monitor again after that the keyboard started working. Go figure. But it would be nice to have a wider choice of boards (the one that's currently working is a skanky old Dell PS/2).

Emuboy 2018-01-04 08:32:07 UTC #84

@Speculatrix , funny enough , I haven't received any notification from this post , I just saw the article on Hack A Day and I came to check the forum .

The schematics are pretty simple, ps/2 is basically i2c , you have clock and data , you can find the schematics here , connect clock and data of your keyboard to the high voltage side of your level shifter (a random one from ebay is good enough) and power that side with 5v (you can take it from the mystom board) and connect the low voltage to the pin on the PMOD feeding the low voltage side with 3v .

be careful with usb to ps/2 adapter, the green one are for mouses and the purple one are for keyboards, they are wired differently!

Folknology 2018-01-04 14:39:14 UTC #85

@Emuboy if you check your preferences you can control notifications etc..

Emuboy 2018-01-04 14:55:34 UTC #86

Thanks, I fixed that

glcraig 2018-01-28 15:14:09 UTC #87

Tried the BBC on my Blackice II board. It works, but the background black comes up green. The rest of the colours seem correct. When you change screen modes, 0-7, it always comes up with white writing on a green background. The game menus are the same. A bit odd. The Atom colours seemed correct. I'm using a TV that has a VGA socket as my LG monitor doesn't do 50Hz.

hoglet 2018-01-28 15:28:57 UTC #88

That does sound odd.

Could you post a couple of photos?

What TV are you actually using?

glcraig 2018-01-28 18:43:22 UTC #89

I'm using a Toshiba Regza LCD. It works the same as the monitor when I tried the Atom on it. It's a bit odd too that the picture is a bit squashed and shifted to the left.

RetepV 2018-01-29 23:31:48 UTC #90

Yaay . Got the BBC B running on my Blackice as well.

I did not have a VGA converter, so as a first step I simply tried to upload the code using dfu-util. That worked fine: but set all the switches to OFF (DOWN), don't forget the jumper. And on a Macbook, use this to program it:

dfu-util -d 0483:df11 -s 0x08000000 -D icebootbeeb.raw --alt 0 -t 1024

As I had no VGA converter, I tested it by long-pressing S4 to see if the blue led would come on. Well, that worked, so I figured that the programming went right. And then I went on to hack a VGA converter. It just uses resistors.

Well, surprise, I got output on my monitor! My monitor is an old laptop LCD screen with a V.59 converter board. And that works great for old game computers and anything with sloppy video signals. Picture works, but it's just slightly unstable. I'll post a schematic a little later.

So next was to hack a PS/2 adapter. And that was a bit more troublesome. The only keyboard that I have is an old 'Mind' clicktey-click keyboard from beginning if the 90's. And it just wouldn't work at 3v3. After long thinking, I read the above comment about the Data and Clock lines being driven open-collector to ground. So I figured that I can simply tie the keyboards VCC to 5V, and keep the rest as it is. Per line a 120ohm resistor in series, and a 2k7 resistor pullup to 3v3. Works great, keys are being recognised fine, and nothing is being fried.

So that's it. Now I have to understand how this BBC B computer works. I never had one myself.

I'll post some pics as soon as I know how.

RetepV 2018-01-29 23:45:30 UTC #91

This is my high-tech schematic of the keyboard interface.

RetepV 2018-01-29 23:48:54 UTC #92

Images of my cobble-up. I'm not proud of it. I'm only proud that I didn't fry the board.

My ancient keyboard, and my limited desk space.

And my first endeavour on a BBC B computer. Same issue with picture squashed and off to the left.

hoglet 2018-01-30 07:25:49 UTC #93

Actually that doesn't look to bad to me.

The "squashed" is possibly expected, as the Beeb is intended to be used on a 4:3 aspect ratio display.

Have you tried using the SD card yet? There's hundreds of great games on there.

You can also wire up sound if you like.

RetepV 2018-01-30 08:11:33 UTC #94

First of all, I meant to write: off to the right, not the left . The drawing area actually extends all the way to the right border of the screen. And if you look at the line, it's slightly less high than it's wide. But I'm nitpicking. And I can center the screen with the monitor's controls. I love this V.59 board. You can get it here, although it's the successor: V.56.

First thing now will be to read some manuals on the BBC computer.

And than there will be sound and cassette, to complete the shield. Don't know how to connect them though. The signal from the FPGA is digital. So I'd need some R/C network for the sound, I presume.

Same for cassette output, I guess. But for cassette input, I think I need to do something to the signal, my guess is a schmitt-trigger type of circuit. Maybe an opamp/comparator that clamps the voltage between 0v and 3v3, and turns the sound waves back into a pwm signal.

hoglet 2018-01-30 09:27:45 UTC #95

The audio output is on PMOD 11/12 pin 9 (that's the top row, and using the MyStorm numbering ). The signal is driven from a PWM DAC inside the FPGA, so ideally you need an external low pass filter. I'm using a 3.3K resistor followed by a 4.7nF capacitor to ground.

The Cassette Interface is not currently implemented.

The best way of loading programs is using the SD Card.

Unzip the following BEEB.MMB file onto a blank FAT32 formatted micro SD card (<32GB).
https://github.com/hoglet67/Ice40Beeb/releases/download/release_1/BEEB.MMB.zip

Then to run it either type *MENU or press shift-break.

Dave

RetepV 2018-01-30 11:44:31 UTC #96

Yeah, I set up an SD card with the .mmb file from the github distribution yesterday. Worked in one go, with an 8GB SD card.

Great job! Tonight I’ll post a quick schematic that I used for the VGA output. This time, I’ll do it the proper way with Eagle.

glcraig 2018-01-30 16:49:09 UTC #97

On the green background. I think it's the TV. I tried the Jupiter Ace and it was fine, (black and white) on my monitor, but it went went green and white on the TV. It was also shifted to the side on the TV only. Strange thing for the TV to do when it has a VGA socket.

RetepV 2018-01-30 22:34:01 UTC #98

As promised, my quickly hacked pmods in Eagle. They work for me, but doublecheck everything before trusting them. For instance, I did not check if the colors are reproduced correctly (maybe I reversed the resistors). In any case, the used resistors don't exactly make a linear DAC anyway. Remember that these are quick hacks with what I had laying around.

Edit: Well, color rendering seems fine, so I guess that I connected the resistors the right way, and the schematics are correct.

uXe 2018-01-31 02:31:36 UTC #99

Did a quick Google, and seems like this is a common complaint (black showing as green on a TV's VGA port). The fix reported by some was to be sure that the cable being used has the actual casing / shield connected to ground - apparently some cables only ground the internal pins and not the actual casing...

hoglet 2018-01-31 08:21:00 UTC #100

Are R13 and R14 really 82K?

This value seems rather high, and might be why your display is shifted to the right a bit.

The Digilent PMOD uses 100R.

Dave