ZXmore or the ZX80CORE follow-up

[Andy Rea]

Today i updated to 1.7 i did not notice any strange vertical lines using a 14 colour tv.

Another question for Karl, can machine code be executed above 32k? I tried the zeddyfox in instance 1 and it just crashed each time.

Regards Andy

[1024MAK]

@ Pokemon, Is it possible to compare the users who built from a complete kit, and those who sourced their own parts. Is there a correlation with the people who have symptoms?

Depending on the results, does a particular chip stand out as being a possible cause due to some internal difference?

Mark

[gemby]

Every now and then i got it to oscillate but it is not stable at all

When i remove IC12 ( HCT125) i have firm 6.410 MHz and notice some activity on led when i connect freq meter across pin 12 and ground and got something on screen ( not a picture, some pattern - bars out of sync, but something is here )

So, when IC12 is removed:
- pin6 of IC21 ( ac86 ) has 6.410 MHz
- pin12 of ( now removed ) IC12 ( hct125 ) has 6.410 MHz
- across R16 i have firm 6.410 MHz

So, is HCT125 have died somehow or it is DOA and it preventing ac86 to oscillate properly? Is it normal to have 6.410 MHz instead of 6.5 MHz?

First the frequency is normal - could be +/- 1 or 2%. This is not very important.
HCT125 is used to maybe stop internal oscillator and to use an external oscillator.

Can you please measure voltage at pin 10, IC12. Should be 5V around.

Yep, it is 5V

And you could measure frequency at pin 12, IC9. Must be half of 6.410 MHz - so around 3.2 MHz.

No, there is nothing there, then i figure out there is no connectivity IC12 pin11 and IC19 PIN11 so i bodged it with wire, after that i finally got stable grey screen

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CLK is the most important thing and you should measure a mixture between 6.4 and 3.2 MHz at pin 6, IC2 (CPU, Z80).

You could remove IC12 completely now when you remove just pin 6 of IC23 and do a resistor (1k to 10k) between pin 4 and 5 of IC8 or just a wire or solder connection. A resistor would be better when you forget later to remove this connection and put pin 6 of IC23 back which would get some hot then with a direct wire.

Yep, tried that, but there was nothing, after i bodged IC12 pin11 and IC19 PIN11 it started to appear.

First goal to measure a valid frequency at pin 6 of CPU. This modification with pin 6 of IC23 would let it run on half frequency (3.2 MHz in your case) and produce a valid video signal if all other is correct.

No, it is only 3.2 MHz, screen is garbled, it reacts to reset, but when i try to measure freq, it usually stop oscillating. When i remove IC12 i got stable perfectly aligned in sync blank grey screen

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So remove IC12, bend out pin 6 of IC23 a little bit out of the socket and make some connection between pin 4 and 5 of IC8 for the first time.
Anyway an oscilloscope would be better than a multimeter.

Yep, this is lousy job to poke around with multimeter :-/

[PokeMon]

Today i updated to 1.7 i did not notice any strange vertical lines using a 14 colour tv.

Another question for Karl, can machine code be executed above 32k? I tried the zeddyfox in instance 1 and it just crashed each time.

Regards Andy

Andy, in general yes - you can execute code above 32k - even above 48k.
But there is a restriction for video driver code which is not possible - for machine code outside video during USR time there is no restriction at all.
There was a problem with z88dk I think using an own video driver above 32k used by siggi.
There would be a hack to allow this but could be done as a hardware mode only (not programmable in the CPLD).

IMG_9001k.JPG (59.97 KiB) Viewed 3424 times

The picture shows the mod. I used a smd pull-up resistor (7k5 I had on my desktop) and soldered it between two CPLD pins here (one has +3.6V) and cutted A15 coming from CPU going to that pin (cutted directly near the cpu) and made a wired-and with two schottky diodes (BAT46) to A15 und A14. This way the video circuit is restricted to addresses >= $C000. The reason for using A15 only as default was the limit of free pins to the CPLD.

So this is an expert hack I would not recommend to all ZXmore owners. But for hardcore users it may be useful.
The 1k resistor above has no meaning here - I just changed another resistor during development and had no chance to cut it out easily from top side.

[PokeMon]

@ Pokemon, Is it possible to compare the users who built from a complete kit, and those who sourced their own parts. Is there a correlation with the people who have symptoms?

Depending on the results, does a particular chip stand out as being a possible cause due to some internal difference?

Mark

As far as i know Mart and Pablo did buy the full kit.
The main important parts are listed which have influence on timing:
IC21=74AC86
IC19=74AHCT74
IC9=74AHCT126
IC8=74AHTC08

All other chips are simply of type HCT. The AC type was used because it can driver higher current for the video output (+/-20mA) by default.

[PokeMon]

And you could measure frequency at pin 12, IC9. Must be half of 6.410 MHz - so around 3.2 MHz.

No, there is nothing there, then i figure out there is no connectivity IC12 pin11 and IC19 PIN11 so i bodged it with wire, after that i finally got stable grey screen

The attachment 2016-01-18 20.20.34.jpg is no longer available

That should be wrong, do you have the schematics ? IC12 pin 11 goto IC9 (!) pin 11, not IC19. Or directly to pin 6 of cpu (CLK).
Both tristate drivers are used to switch between the two frequencies 6.5 MHz and 3.25 MHz during video display:

Bildschirmfoto 2016-01-18 um 23.11.40.png (52.2 KiB) Viewed 3423 times

The reason why you get a response from the cpu is that you placed this wrong wire which feeds cpu directly with 6.5MHz clock. It is likely that the oscillator will stop if you place a higher capacity / lower resistor to its output. The reason for the grey synced picture is that the horizontal syncs are created automatically from the 6.5 MHz clock. What signal do you have at pin 13 of IC12 ? Maybe this is a dead driver - this way you can do the mod i described earlier to fix the frequency to 3.25 MHz for a first start.

Good luck again.

[gemby]

And you could measure frequency at pin 12, IC9. Must be half of 6.410 MHz - so around 3.2 MHz.

No, there is nothing there, then i figure out there is no connectivity IC12 pin11 and IC19 PIN11 so i bodged it with wire, after that i finally got stable grey screen

2016-01-18 20.20.34.jpg

That should be wrong, do you have the schematics ? IC12 pin 11 goto IC9 (!) pin 11, not IC19. Or directly to pin 6 of cpu (CLK).
Both tristate drivers are used to switch between the two frequencies 6.5 MHz and 3.25 MHz during video display:

Bildschirmfoto 2016-01-18 um 23.11.40.png

The reason why you get a response from the cpu is that you placed this wrong wire which feeds cpu directly with 6.5MHz clock. It is likely that the oscillator will stop if you place a higher capacity / lower resistor to its output. The reason for the grey synced picture is that the horizontal syncs are created automatically from the 6.5 MHz clock. What signal do you have at pin 13 of IC12 ? Maybe this is a dead driver - this way you can do the mod i described earlier to fix the frequency to 3.25 MHz for a first start.

Good luck again.

Thank you Karl, i connected pin11 ic19 and pin12 IC12 sry for confusion, ( look picture of board ) , since there was no connectivity, and by schematics, it has to be, i will double-check everything once again and post update.

[martinjharvey]

Hi Karl,

I've tried uploading some photos of my ZXmore but the board says the limit for attachments is reached. So instead I've zipped them up for download here
http://www.martinjharvey.com/ZXmore.zip

I've checked the capacitor that you mentioned and it appears to be the correct one installed in the correct place according to your build instructions. I am experiencing a colour effect when using my ZXmore on a 32" Samsung but on a cheaper Bush TV (maybe 14" screen) the display is stable yet the entire screen seems shifted over to the right by about an inch. Not sure whats happening but this occurred before the update and is still present now. The pictures I've taken show it better than I can say it

The colour/rainbow effects were difficult to capture but they can be seen on the close up of the ZXMaster instance that I took.This effect is now not present in the ZX81/80 instances as it was prior to the 1.7 update, just the ZXMaster instance. I have replicated this effect on my actual ZX81 that has your ZX8-CCB installed, so it could be some sort of sync issue. I can tweak it out of my ZX81 and get a stable clear picture on both TV's however using the ZX8-CCB trimmers.

One other thing I've noticed is that when I enter an instance, say ZX81 instance 1, the inverted K cursor has the K shifted to the bottom of the inverted square(photo in zip). The same is also true when entering a program and the inverted current line cursor is the same! This does however correct itself if I DS-C the instance for compatibility mode.

Apart from these niggles everything else is groovy

Mart

PS. You were right, I did have the full kit from you

[Andy Rea]

Andy, in general yes - you can execute code above 32k - even above 48k.
But there is a restriction for video driver code which is not possible - for machine code outside video during USR time there is no restriction at all.
There was a problem with z88dk I think using an own video driver above 32k used by siggi.
.

ahah, that will be why it crashed then, siggi wrote the zeddyfox using z88dk

thanks, i might try the mod, i think i have some shotky diode in my bit box

andy

[PokeMon]

Thanks Mart, I will check it out soon and try some things myself in the next days.