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Old 7th Nov 2022, 9:08 am   #101
microlan
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Default Re: Yet another MK14 vdu card

Hi all!

I am new user in these forum. My name is Milan Humpolik. I wrote the code for game PONG. Thanks to the member here for editing and publishing. Thank you for creating code for SPACE INVADERS!

My MK14
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Old 7th Nov 2022, 10:24 am   #102
SiriusHardware
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Default Re: Yet another MK14 vdu card

Hello Milan, we already know about you of course, so it is good to see you here in our forum.

As well as Milan's PONG game which was recently translated to SBASM3 format by Realtime, Milan also made an interesting MK14 uploader / keypress recorder, the story of which can be read about in this forum thread (english readers will need to let their browser translate).

http://oldcomp.cz/viewtopic.php?p=70841#p70841
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Old 7th Nov 2022, 12:13 pm   #103
Phil__G
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Default Re: Yet another MK14 vdu card

Here you go

https://www.youtube.com/watch?v=KFI_XQRYK-A
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Old 7th Nov 2022, 7:36 pm   #104
Realtime
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Default Re: Yet another MK14 vdu card

Quote:
Originally Posted by microlan View Post
Hi all!

I am new user in these forum. My name is Milan Humpolik. I wrote the code for game PONG. Thanks to the member here for editing and publishing. Thank you for creating code for SPACE INVADERS!

My MK14
Hi Milan, great to see you on the forums. That's a really nice motherboard/backplane you created. I assume that's a RAM expansion module plugged in the top?

Are you planning any other add-ons?
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Old 8th Nov 2022, 8:27 am   #105
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Default Re: Yet another MK14 vdu card

Yes, it is extended RAM 1,5 kB with 6116. I have nothing planned. But currently I have a stepper circuit in the last position. Maybe any D/A converter for audio in distant future.
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Old 11th Nov 2022, 11:59 am   #106
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Default Re: Yet another MK14 vdu card

My 'Realview' is here! Thanks Ian.

Unfortunately (as normal) I am away for the weekend and won't be able to play until next week. Looks very nicely put together though.
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Old 11th Nov 2022, 6:49 pm   #107
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Default Re: Yet another MK14 vdu card

Here's the Tech Notes for the RealView VDU card and DM8678 Emulator modules. It's aimed at giving enough info to understand the operation of the cards and perhaps make modifications (at your own risk ). It's not a resistor-by-resistor description, but if you need any clarifications then let me know.
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Old 11th Nov 2022, 9:27 pm   #108
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Default Re: Yet another MK14 vdu card

Thanks Realtime: I've just quickly scanned through it - it looks very flexible in the way you have arranged for the control lines to be controlled by (mainly) 8154 port B or force-set by switches.

One thing I do notice though - when Realview is to be used in the basic 640 byte 'legacy' mode for which most of the old 'demo' programs like 'Falling Man' were written, there is (usually) an assumption that the screen upper half will display the contents of 0F00-0FFF and the lower half of the screen will display the contents of 0B00-0BFF.

In order for that to happen the 'X' Portion of address 0X00 needs to be alternated between 1111 (F) and 1011 (B), so you then need to be able to connect TOP PAGE to address select input PS3, which I don't immediately see any allowance for at the moment, rather than TOP PAGE to PS1, which is allowed for.

This could be a problem for someone who has a 640-byte issue II, III, or IV where the extra RAM which Realview can provide at 0200-07FF can not be enabled because it would clash with the PROM images, leaving the standard and optional RAM as the only memory available to use as display RAM.
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Old 11th Nov 2022, 11:04 pm   #109
Realtime
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Default Re: Yet another MK14 vdu card

Ok thanks Sirius, I can see what you mean. Looks like it would need an extra switch to be connected between SW1 pin 11 and SW1 pin 18 to do that, or cut a track and repurpose the bottom switch to PA3.
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Old 12th Nov 2022, 1:48 am   #110
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Default Re: Yet another MK14 vdu card

On any future revision of the PCB maybe just make the destination of the output of A_SW10 selectable with a 2x4 pin array onto which a single 2-pin PC style jumper (like the ones fitted on the char gen PCB) can be fitted. (see crudely modified diagram section below).

Alternatively 5 pins arrayed in a cross shape where the jumper goes between the centre pin and one of the outer ones - fewer pins needing less space, has the merit of ensuring that only one jumper can be fitted but would require a row of 3 pins to be soldered in, and then two single pins to be soldered on either side of the centre pin.

Alternatively, assume that PS1 and PS3 are the only selections actually likely to be made, omit the choices of PS2 and PS4 and have a square block of only four pins allowing A_SW10 to be routed via a single 2-pin jumper to PS1 or PS3.
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Old 12th Nov 2022, 9:40 am   #111
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Default Re: Yet another MK14 vdu card

Obviously the third option (four pins in a square) could be boiled down to three pins in a row, with the feed from A_SW10 going to the centre pin, the outer pins going to PS1 and PS3 respectively.
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Old 12th Nov 2022, 10:33 am   #112
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Default Re: Yet another MK14 vdu card

Having thought about it a bit more perhaps the neatest solution would be to re-purpose SW10 as the 'split graphics / characters' enable switch, and have the TOP PAGE to PS1 / PS3 selection on a three pin two position header, as shown (attached).

In the unusual event that the user really does want to show the same 256-byte RAM region on both the upper and lower halves of the screen the jumper can be taken off or 'parked' sideways on the centre pin so that it does not route TOP PAGE to either PS1 or PS3.
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Old 12th Nov 2022, 11:37 am   #113
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Default Re: Yet another MK14 vdu card

Something else to look into:

With the circuit as drawn the TOP PAGE output from the CPLD doesn't appear to have a 'safety' resistor in series with it, so if switch SW1 is turned on, shorting MK14_PS1 to 0V, then SW10 is also turned on to connect TOP PAGE to MK14_PS1, TOP PAGE will be hard shorted to 0V via SW10->SW1. I don't know how well the CPLD would be able to tolerate that situation?
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Old 12th Nov 2022, 3:10 pm   #114
Realtime
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Default Re: Yet another MK14 vdu card

You have a very good point. The CPLD doesn't seem to suffer. I was running it driving into ground for a few weeks before I realised . I had alluded to this on page 4 of the Tech Notes in red text, but didn't explain why (typical tech author behaviour in my experience).

Looking at the layout I think the best thing to do is cut the track marked with a red arrow in the photo (breaking the PS1 connection between SW1-10 and SW1-20) and add a 1K resistor on the back of the board from SW1-10 to SW1-20. That provides TOPPAGE protection from PS1 being grounded.

(Alternately connect the resistor from SW1-18 to SW1-10 to provide the PS3 video page swapping mentioned in post 108).

For using the split graphics / character mode a 1K resistor should be inserted in the spare pads of SW2-10 and SW2-11. That then provides TOPPAGE protection from MK14_GR_nCHAR being grounded.

Luckily the owners of the 3 modules already sent out are all skilled in electronics so I hope will be happy to make the mod's . I'll apply the changes to future ones and update the Tech Notes to reflect the change. I have just made the mod on my one and it works fine.

Thanks for all the suggestions on TOPPAGE to PSx connections. They'll go in the Future Mod's bucket, if there ever is an update to the board.
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Last edited by Realtime; 12th Nov 2022 at 3:14 pm. Reason: Added info
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Old 12th Nov 2022, 6:22 pm   #115
Realtime
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Default Re: Yet another MK14 vdu card

Way back at the start of this thread Tim asked
Quote:
Originally Posted by Timbucus View Post
Do you have a chip fab and can you make 74L86
I don’t! But there is a guy in the Netherlands selling NOS 74L86’s, in case you haven’t seen it. £3 each and reasonable postage to the UK.
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Old 12th Nov 2022, 8:54 pm   #116
SiriusHardware
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Default Re: Yet another MK14 vdu card

Thanks for looking into that and documenting an approved 'TOP PAGE saver' mod.

For my own purposes, I may still do a further mod to allow jumper link setting of TOP PAGE through to either PS1 or PS3 to make it easier to switch between 'legacy' VDU programs written to run in onboard RAM and newer ones like INVADERS which utilise two consecutive 256 byte blocks in the 0200-07FF RAM area. I don't really want to hard wire it one way or the other. On my interconnection / RAM board which goes between the issue VI and my real SOC VDU, and on Ortonview, I switch back and forth between those two configurations quite often.

Last edited by SiriusHardware; 12th Nov 2022 at 9:19 pm.
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Old 12th Nov 2022, 9:15 pm   #117
SiriusHardware
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Default Re: Yet another MK14 vdu card

Quote:
there is a guy in the Netherlands selling NOS 74L86’s
Better get about half a dozen, Tim. A year's supply, give or take...
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Old 14th Nov 2022, 6:20 pm   #118
Timbucus
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Default Re: Yet another MK14 vdu card

Quote:
Originally Posted by SiriusHardware View Post
Quote:
there is a guy in the Netherlands selling NOS 74L86’s
Better get about half a dozen, Tim. A year's supply, give or take...
Yea OK ha ha very funny...
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Old 14th Nov 2022, 6:24 pm   #119
SiriusHardware
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Default Re: Yet another MK14 vdu card

Just Joshing, you know that.

I should hopefully get a chance to fire up my Realview later on.
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Old 14th Nov 2022, 9:07 pm   #120
SiriusHardware
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Default Re: Yet another MK14 vdu card

Realtime - where control lines are only expected to be driven by a port pin or forced low by the switch, those lines have a BAT48 Schottky diode (only) between the associated 8154 port pin and the switch / pullup resistor / control input.

In the case of control lines which could also (potentially) be driven by TOP PAGE (Graph/Char, MK14_PS1) you have post-inserted a 330R resistor in series with the BAT48.

If we route TOP PAGE to MK14_PS3 either permanently or via a switchable arrangement, should we also make the same change on the MK14_PS3 line, that is, insert a 330R resistor in series with the BAT48 diode on MK14_PS3?
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