πŸ‡¬πŸ‡§ Sinclair ZX Spectrum: Part 5 (RGB cable & more diagnostics) [TCE #0511]

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Progress? It has been known to occur occasionally on my channel.

I decided to switch from composite video output to RGB via vRetro's vLA82. Thus I made up an 8-pin DIN RGBS cable.

It has the same pinout as the cable for the Spectrum +2A, but no need for mono-audio in the cable as the vLA82 provides that via a standard 3.5mm socket next to the DIN socket.

So the pinout is:

Pin 2 = ground
Pin 4 = sync
Pin 6 = green
Pin 7 = red
Pin 8 = blue
(other pins remain unconnected)

I have the Retroleum diagnostic ROM installed on the Speccy board in place of the Sinclair ZX Spectrum ROM. And ... the text is readable now! Well, after a cold boot. Once the machine has warmed up a little it starts misbehaving.

http://blog.retroleum.co.uk/electroni...

So finally I have something concrete to work with - it still does appear to be an addressing issue with the lower 16KByte of RAM (where the screen memory is).

Time to do some research ...

Photos on my Patreon (free or paid members):
https://www.patreon.com/posts/zx-spec...

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From Part 3:
Ivan very kindly donated one of his 128KByte RAM expansion boards so I am looking forward to trying that out - my first package from πŸ‡·πŸ‡Έ Serbia! In order for it to work you need to disable the upper 32KBytes of internal RAM, which I've done by adding a switch to inhibit the !CAS signal for that bank of RAM (make one OR gate input on IC23 always HIGH by connecting to +5V thus forcing the output HIGH, thus disabling !CAS).

I've verified the switch works by executing "PRINT PEEK 23732 + 256 * PEEK 23733" : I get 65535 (full 48KBytes), or 32767 (upper 32KBytes disabled).

However, after this it seems things started to go awry (nothing to do with Ivan's board).
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Music by Karl Casey @ White Bat Audio
https://karlcasey.bandcamp.com
Β Β Β /Β @whitebataudioΒ Β 



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