BBC Model B implementatation for myStorm BlackIce

[tony1tf]

Wow - it works - I saw that the up position said ON, but for some reason I thought that was not being pulled down by the switches. Mind you, I tried them in both positions earlier, but perhaps I have "cleaned" the filing system since.

Tony

[tony1tf]

I've got some weird colour mapping - here is a picture of the Elite start-up screen - strangely most of the colours look the same as Dave's on this photo taken with my phone, but when I look at my VGA screen, the top part is OK, but the bottom part shows purple instead of white, red instead of orange and dark blue instead of light blue. Changing the brightness and contrast on the monitor doesn't make any difference. It must be flickering at a rate that makes the photograph different from my eyes.

Tony

[tony1tf]

Now got sound working - it seems to be on PMOD12 pin 8, not 9 as Dave states earlier.
Tony

[hoglet]

There is a huge potential here for confusion regarding pmod pin numbering, as the connector on the BlackIce schematic is numbered completely differently to the way that Digilent number their Pmod connectors.

The numbers I have quoted are consistent with the BlackIce schematic.

See diagram below:

I wonder if this also explains the colour differences.

[tony1tf]

Hi Dave

Oh my goodness! - I have notes from the Chiphack2017 event which I was working from, and they seem to be consistent with Digilent - in fact the audio is on pin 2 in that nomenclature. I had reversed top and bottom when I said pin 8.
My Veroboard layout for the VGA Adaptor is tightly linked to the Digilent pinout. Maybe a tweak to the verilog is easier? Need to get this all squared for newbies not to get confused.

Tony

[Folknology]

I Think Digilent decided to number the pins against the standard right angle dual row pinout numbers from memory, that may account for differences...

[Folknology]

If it is a CRT monitor it may need degaussing, otherwise maybe a signal/cabling problem

[hoglet]

Maybe a tweak to the verilog is easier? Need to get this all squared for newbies not to get confused.

I think that would actually make things worse!

At the moment, the connectivity is consistent with the Digilent PMOD adapters. It's just the convention for pin numbering that's different.

I'm going to stick with using the BlackIce numbering, and if the powers that be decide to change that, I'll follow suit.

Dave

[tony1tf]

Hi
No - its an old 4:3 LCD monitor by Medion. It's got a built in speaker which is good for the sound.
Tony

[tony1tf]

On a different tack, I just typed in the Sphere benchmark. When I tried to save it, it said "Disc read only". Is that a future project?
Tony

[hoglet]

On a different tack, I just typed in the Sphere benchmark. When I tried to save it, it said "Disc read only". Is that a future project?

It likely means the current disc image is locked (protected).

Try typing:

 *DOP U

to unlock, then you should be able to save.

There is some documentation for MMFS here.

Dave

[tony1tf]

Thanks Dave
Now have a working DFS.
One more question - I have a several Microvitec monitors - is the sRGB o/p you mention suitable for them? and what pins to use. I'm sure I can put a scope on the outputs and find out for myself, but it's probably quicker if you tell me.
For the future: At some time, I will probably want to use the BBC 1MHz bus, so is that something you might be working on?
best regards
Tony

[hoglet]

One more question - I have a several Microvitec monitors - is the sRGB o/p you mention suitable for them? and what pins to use. I'm sure I can put a scope on the outputs and find out for myself, but it's probably quicker if you tell me.

There's a couple of things to be (very) wary of:

1. The outputs from the FPGA are not guaranteed to be able to drive TTL levels, so some kind of level shifter might be needed, which would also serve to protect the FPGA board. That's assuming your monitor is expecting TTL levels. Do you know the input level specifications?

2. Ice40Beeb defaults to VGA, and it's possible that the 31.25KHz VGA would cause damage to the monitor. I would look to disable the VGA mode to be safe.

Honestly, I would say an old LCD TV with a SCART input would be a safer bet. But it really depends on your level of competence here.

In both cases, the pins to use are:
R = PMOD 9/10 pin 5
G = PMOD 7/8 pin 5
B = PMOD 9/10 pin 6
Sync = PMOD 7/8 pin 12

(Pin numbers are BlackIce pin numbers, see diagram above)

For the future: At some time, I will probably want to use the BBC 1MHz bus, so is that something you might be working on? best regards

The 1MHz bus is already present internally in the FPGA, so bringing the signals out to the PMOD connectors would be possible. But again, the levels are not TTL levels, so some kind of level shifter would be required to be electrically compatible with original devices.

What device were you hoping to hook up?

Dave

[tony1tf]

Hi Dave

I missed out the buffer on my veroboard version of the PMOD to VGA adaptor, and it works OK.
I presume the Micovitec monitor doesn't require heavier driving. When you say that the FPGA can't drive TTL, is that the current sink, because the 3V3 "1" level should be fine for 5V TTL?
I have both TTL and analogue input monitors, and TV's with SCART.
On the 1MHz bus, I have things like 1MHz bus to STE adaptors, although it might be going a bit far to dig out stuff out of my junk piles that I havn't touched for decades. Until retirement, I used to work at Leicester University Space Research Centre, and in the early days used the Atom and then BBC Micro to drive CAMAC racks for calibration of UV and X-ray detectors. So I explored all the commercial interfaces you could use with BBC's then RiscPCs. I shuldn't get too enthusiastic - there's not enough time, really!

Tony

[hoglet]

I presume the Micovitec monitor doesn't require heavier driving. When you say that the FPGA can't drive TTL, is that the current sink, because the 3V3 "1" level should be fine for 5V TTL?

It may well work fine.

I've seen some monitors whose inputs are terminated with 75 ohms, and driving those (while still maintaining TTL levels) might be harder.

Anyway, the specifications for the monitor should clarify this.

If it were me, I'd probably give it try.

Dave

[tony1tf]

I mentioned using a Microsoft Keyboard, with keys that needed remapping. I have just been sticking labels on the keys, so that it is a bit easier to type in BASIC programs etc. Here's a picture, in case anyone else out there needs to use a modern keyboard. The "most" important one is the "End" key which is the BBC editing function "Copy" key.

Tony

[tony1tf]

Hi Dave

Thanks for the info. It works perfectly - I fed the sync, and RGB through 100 ohm resistors to protect the FPGA. Really nice quality on an old Microvitec monitor as in the picture here. The picture is square - my camera was at an angle

Tony

[hoglet]

That's really good to see.

[tony1tf]

Hi Dave et al

Although I used separate 100 ohm series resistors for driving the Microvitec at first, I have just changed the configuration - the Microvitec cable can connect to the VGA connector with some tail wires - there is already a series 100 ohm in sync, and the DAC resistors are also OK (470 ohm in my circuit, 536 ohm in the Digilent design). So the connections are:
Microvitec VGA
Red----------1
Green-------2
Blue---------3
Ground-----5
Sync-------13
I have tried two TTL input Microvitecs and both work fine with this arrangement.

On a different matter - regarding disc images, I note that there is a BBC emulator on the web which uses .ssd files. Do you know how these can be made compatible with the .MMB file. I looked at the .MMB file with a hex viewer after I had been using it in the BlackIce board and see it is a complete image - now incorporating the Basic program I saved. I was hoping I might see the saved file separately, so I could add a new image from my Mac.

Tony

[BigEd]

There's a suite of command line tools written in perl which do a good job of manipulating MMB files: as you've guessed, an MMB file is a structure which contains a number of SSD images. With the tools you can put and get the SSD images, and unpack and repack the files within those images. See here:

hoglet67/MMFS

I use the 'beeb' command to do everything - alternatively you can run individual perl scripts.

$ ~/MMFS/tools/mmb_utils/beeb 
Syntax: beeb command [args]
  Possible commands:
    access
    blank_ssd
    compact
    daccess
    dblank_mmb
    dcat
    delete
    dform
    dget_ssd
    dgetfile
    dinfo
    dkill
    dlabel
    donboot
    dput_ssd
    dump
    getfile
    info
    list
    merge_dsd
    opt4
    putfile
    rename
    split_dsd
    title
    type