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Old 4th Mar 2023, 2:14 pm   #1
DavidMS
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Default MK14 Alternative VDU concept

I have been looking at constructing a Orton View, but am struggling to find a a VDU with a composite video interface (by this mean I know I have one in the loft but who knows where it has vanished to). I have a few old Dell PC monitors but all the existing VDU designs seem to output composite.

So my thought is to use an Pi Zero with it's HDMI output interfaced to a suitable RAM, mapped to relevant areas on the MK14 (as per the Orton view). But rather than the Pi address it directly add a bit of glue logic to free the Pi up from the timing constraints of accessing the RAM. So in practice the Pi 'requests' a given byte of RAM which it displays as a sudo mapped display window. The Pi does not need to sync reads to the video update rate as the internal HDMI h/w covers that. All it needs to do is to read the video ram area fast enough so there is no perceptible delay the to person viewing the HDMI monitor - which I can probably do in Python, certainly in C++

My question is has this approach been looked at before ? I know there is a RC2014 board that does a similar thing but that is really just a serial terminal, so would not work with existing MK14 s/w which is my goal.

I do also realise that I could do the whole thing with a Pico using it's PIO capability but programming of this is currently beyond me - I get the video out element but not how I would get data into to the Pico asynchronously

Anyway would be interested in peoples thoughts
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Old 4th Mar 2023, 2:25 pm   #2
ortek_service
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Default Re: MK14 Alternative VDU concept

You could always just use one of those (Around £15?) RGB/Composite to VGA boards or SCART to HDMI converter boxes
(These also do the scan-rate conversion so don't require a monitor that works down to 15.625kHz / 50Hz)
Or use an old DVD etc recorder, that has HDMI Output

I seem to recall you can also get small LCD >=5" modules, that will accept composite-in, for not too much more.
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Old 4th Mar 2023, 2:28 pm   #3
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Default Re: MK14 Alternative VDU concept

Quote:
So my thought is to use an Pi Zero with it's HDMI output interfaced to a suitable RAM, mapped to relevant areas on the MK14...
Coolnaz2 has already done something remarkably close to this, using a dual-port RAM as the interface between the MK14 and in his case the Raspberry Pi.

The dual port RAM is mapped at 0200-07FF on the Mk14, to which it just appears as normal RAM. The MK14 can read from or write to it as usual.

The Pi (or whatever you choose to use) reads the screen memory content out through the secondary port of the RAM and in Coolsnaz's case renders it to a window on his HDMI-connected Raspbery Pi.

The advantage of this method is that the VDU doesn't have to halt the SC/MP in order to read from the screen RAM - the SC/MP can keep running at full speed.

Ah, here it is:

https://vintage-radio.net/forum/showthread.php?t=193351

The thread has been automatically closed due to inactivity but you can make a polite request to the mods if you want it re-opened.
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Old 4th Mar 2023, 3:03 pm   #4
DavidMS
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Default Re: MK14 Alternative VDU concept

Quote:
Originally Posted by ortek_service View Post
You could always just use one of those (Around £15?) RGB/Composite to VGA boards or SCART to HDMI converter boxes
(These also do the scan-rate conversion so don't require a monitor that works down to 15.625kHz / 50Hz)
Or use an old DVD etc recorder, that has HDMI Output

I seem to recall you can also get small LCD >=5" modules, that will accept composite-in, for not too much more.
Yes, I had looked at the composite to VGA boards, but if I am going to build something not sure of the advantage of going that route, I can also take advantage of a fast SRAM chip to minimise the time the MK14 is 'suspended' .
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Old 4th Mar 2023, 3:08 pm   #5
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Default Re: MK14 Alternative VDU concept

The MK14 doesn't have to be suspended at all if you use dual-port RAM as per Coolsnaz2's scheme.
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Old 4th Mar 2023, 5:50 pm   #6
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Default Re: MK14 Alternative VDU concept

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Originally Posted by SiriusHardware View Post
The MK14 doesn't have to be suspended at all if you use dual-port RAM as per Coolsnaz2's scheme.
Yes, I knew of dual port rams existence but have never has cause to use them. I think I will go down that route as it makes everything very simple. It did not look like Coolsnaz2 uploaded their code but it should be fine to build in stages - and even more positively RS have the PDIP version in stock so building on vero will be a bit easier - not the cheapest of devices @ £18 but that can be set against not needing additional buffer chips etc
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Old 4th Mar 2023, 6:23 pm   #7
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Default Re: MK14 Alternative VDU concept

It's a bit of a monster (48 pin). Can you still get 48-pin DIP sockets I wonder?

I bought one years ago with a view to putting it between my original MK14 which only ever had the official 640 bytes on board and my original SOC VDU but my natural inertia / laziness is so severe that events eventually overtook me and I ended up with an issue VI + Ortonview, both PCBs courtesy of Slothie, and then a Realtime 'Realview' as well.

Coolsnaz2 is still very active here but just lately he has been more focused on his fast loading system for the MK14 - the last time he wrote about the Pi-VDU was to say that he didn't really feel it was polished enough to show off at the retro computer fair at the Centre For Computing History towards the end of last year. One thing he did mention was that the RAM reading / rendering software (written in Python I believe) had quite a slow refresh rate (17fps is the figure I think he mentioned) but if you feel you could do it in 'C' or even baremetal ARM assembly language then don't let us stop you.

I know from my own experience that it's always easier to keep going on a project if there seems to be more than just myself that is interested in seeing it finished, so maybe drop Coolsnaz2 a PM about it or ask for his thread to be re-opened?
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Old 5th Mar 2023, 12:36 pm   #8
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Default Re: MK14 Alternative VDU concept

Quote:
Originally Posted by SiriusHardware
It's a bit of a monster (48 pin). Can you still get 48-pin DIP sockets I wonder?
I used 2 x 24 pin sockets.

I have not done any work on the Pi based MK14 VDU for a few months now. The problem I have is the occasional conflict between the MK14 and Pi, I assume it's when both are trying to access the same memory location. This can be seen in the attached photos, currently I am not using the busy pin on the IDT7132.

I fixed the problem with vertically stretched heads in fallman, just made my pixels square.

I can post my python code here if required but it is still at a testing and develop stage with very little comments.
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Old 5th Mar 2023, 12:48 pm   #9
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Default Re: MK14 Alternative VDU concept

Quote:
I used 2 x 24 pin sockets.
Of course..(slaps forehead at the simplicity of the idea).

If you think there are problems arising from the MK14 and the Pi trying to access the same location at the same time I suppose you could just adopt the same method as the other hardware VDUs do - assert NENIN to halt the SC/MP during screen memory access, but it would be a pity to have to throw away that nominal advantage of using a dual port RAM in the first place.
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Old 6th Mar 2023, 12:45 pm   #10
DavidMS
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Default Re: MK14 Alternative VDU concept

Quote:
Originally Posted by coolsnaz2 View Post
Quote:
Originally Posted by SiriusHardware
It's a bit of a monster (48 pin). Can you still get 48-pin DIP sockets I wonder?
I used 2 x 24 pin sockets.

I have not done any work on the Pi based MK14 VDU for a few months now. The problem I have is the occasional conflict between the MK14 and Pi, I assume it's when both are trying to access the same memory location. This can be seen in the attached photos, currently I am not using the busy pin on the IDT7132.

I fixed the problem with vertically stretched heads in fallman, just made my pixels square.

I can post my python code here if required but it is still at a testing and develop stage with very little comments.
I would appreciate having a look at your code - fully understand it is work in progress

My plan is to use the busy pin to avoid conflicts as you suggest
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Old 6th Mar 2023, 12:52 pm   #11
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Default Re: MK14 Alternative VDU concept

A question on memory the logical choice is the IDT7130SA/LA which I can easily get from RS as DIL device. But this is a 1Kx8 device, there is a 2kx8 version but is currently harder to find - Mouser have it as a 53pin PLCC, but the obvious UK people don't seem to have stock.

So how much existing s/w am I not not going to be able to run by limiting the expansion to 1k rather than 1.5k ?. Clearly the copycat game would be a problem but what else ?

David
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Old 6th Mar 2023, 1:53 pm   #12
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Default Re: MK14 Alternative VDU concept

What is the 2K device you are trying to find? (what number?) 7132, or...?
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Old 6th Mar 2023, 2:19 pm   #13
DavidMS
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Default Re: MK14 Alternative VDU concept

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Originally Posted by SiriusHardware View Post
What is the 2K device you are trying to find? (what number?) 7132, or...?
Yes - have just found the 2k version on eBay so will give it a go- they are coming from Poland but hopefully will be ok
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Old 6th Mar 2023, 3:00 pm   #14
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Default Re: MK14 Alternative VDU concept

I'll have a look at mine (the one I never used) tonight and if it is a 48-pin PDIP 2K IDT7132 you can have it, as I am unlikely ever to use it now.

However, maybe it's not a good idea to base a new design on something which appears to be unobtainium. If you think about it only 512 bytes of the RAM - 0200-03FF - actually needs to be dual-port, that's if we stick with the convention that the screen RAM on an MK14 with RAM mapped at 0200-07FF will always be 0200-03FF. It's not a bad idea to pick a standard and stick with it so we don't have to twiddle the address block selectors on our VDUs every five minutes.

If you don't mind the chip count going up a bit you can map the 'obtainable' 1K dual port RAM at 0200-05FF and then fill in the missing 512 bytes with a more conventional RAM.

Edit: Arrgh! Didn't see your post above until I had hit 'submit' on this one, sorry.
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Old 6th Mar 2023, 3:31 pm   #15
SiriusHardware
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Default Re: MK14 Alternative VDU concept

Quote:
I can post my python code here if required but it is still at a testing and develop stage with very little comments.
I would suggest you don't post what you feel is unfinished code in a public post, but instead get in touch with each other via PM. You can't exchange files by that medium but you could exchange email addresses and take it from there.
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Old 6th Mar 2023, 7:49 pm   #16
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Default Re: MK14 Alternative VDU concept

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Originally Posted by DavidMS View Post
So how much existing s/w am I not not going to be able to run by limiting the expansion to 1k rather than 1.5k ?. Clearly the copycat game would be a problem but what else ?
Invaders (v1 and v2) needs the full 1.5K expansion and I've got 2 more games in the pipeline that will definitely need the full expansion (and the base RAM at 0xB00 and 0XF00) [ a little teaser for you there ].

NIBL uses a lot of RAM too. I'm sure Phil_G can tell us exactly where it's located.
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Old 6th Mar 2023, 9:33 pm   #17
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Default Re: MK14 Alternative VDU concept

You realise you're now the most prolific coder of full programs / applications for the MK14 since whoever put the original programs for the user manual together?

I have no idea what it is you have in the pipeline but I think the pixel graphics mode of the VDU would lend itself quite well to a version of the PONG game as presented on the AY-3-8500 based 'TV game' consoles.
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Old 6th Mar 2023, 9:40 pm   #18
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Default Re: MK14 Alternative VDU concept

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Originally Posted by Realtime View Post
NIBL uses a lot of RAM too. I'm sure Phil_G can tell us exactly where it's located.
Original NIBL occupies 0000-0FFF, NIBLE the Elektor version was relocated I think to 1000-1FFF. I’m not sure about the ram used for basic programs etc.
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Old 6th Mar 2023, 10:35 pm   #19
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Default Re: MK14 Alternative VDU concept

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Originally Posted by SiriusHardware View Post
You realise you're now the most prolific coder of full programs / applications for the MK14 since whoever put the original programs for the user manual together?
I agree !

Quote:
Originally Posted by SiriusHardware View Post

I have no idea what it is you have in the pipeline but I think the pixel graphics mode of the VDU would lend itself quite well to a version .....
Well, when I looked at the 3rd image, I immediately thought 3D Monster Maze !
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Old 6th Mar 2023, 10:42 pm   #20
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Default Re: MK14 Alternative VDU concept

I actually missed the launch of Realtime's 'Maze' game altogether, I don't know if it wasn't given the same launch 'treatment' as Invaders but somehow it got past me.

I've always loved '3D' maze games going all the way back to one that someone I knew had on the TRS-80, and of course 3D Monster Maze was the ZX81's 'Killer App'. I don't know if it would be feasible to port 3DMM to a ~2K MK14, considering that the original needed a 16K ZX81.
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