Sinclair ZX80 / ZX81 / Z88 Forums

For those who have a monitor that can cope with RGB video (Hsync @ 17.5Khz) like Samsung 510n. Here you are a circuit buit to allow to choose the foreground and background colors for ZX81 video using dip switches. Need separate positive sync, though.



Further details http://danjovic.blogspot.com.br/2015/05 ... r-rgb.html
Cable, schematics and single sided board http://danjovic.blogspot.com.br/2015/05 ... olour.html

Very nice! I really like the red-on-black. Very Sinclair.

Should be relatively easy to implement by the ZX80/ZX81 clone builders among us, especially if video (without sync) and sync are readily available to pick up in the circuit. Like in my very own ZX81 ULA replacement...

But you could also pull sync from a comp. video signal using a sync splitter, say an LM1881 or similar. Shouldn't be too difficult. And perhaps even feed the unmodified video signal into an R/G/B input. After all, ZX81 video doesn't contain any color info, so it's basically a luminance signal with the sync tacked onto it. With a bit of luck the screen image wouldn't be distorted (too much) even if the sync signal is still included. Otherwise use a bit of circuitry to remove sync pulses from the comp. video signal.

Btw: I'd go for a dark/light amber scheme myself. Used to have an amber monochrome monitor once. Sold it off some day as it saw little use & I needed the space. But there have been days I wish I still had it. These days: nearly impossible to find/amber but not comp. video/monochrome, but green instead of amber/too expensive/shipping costs too high/still need the space.

Sadly even a good RGB monitor can't achieve the image quality of a true monochrome monitor (uniform phospor layer vs. RGB dots, and things like that). But it's a better-than-nothing substitute for us monochrome addicts.

Beautiful! Sirmorris you're right. The red character on a black background smashes!!!
Good job, Danjovic!
You could attempt to add a circuit like this (or similar):
So the colors could be managed from BASIC.
If you need, I have the full article.

Thanks!

The main goal of the project is to allow to user to stick at the most pleasant color combination (fixed color configuration), but yes, I think is posible to perform the color selection by a poke, preferably by activating a latch using the ROM CS, thus allowing to type "POKE 0,nn" and change the colors.

[]s
Danjovic

Be aware that the first five bytes of the rom are being written to by the floating point routines of the rom.
So using poke 0,color would result in unpredictable color changes

Kind regards
Paul

Paul wrote:Be aware that the first five bytes of the rom are being written to by the floating point routines of the rom.

Not only floating point, a simple PRINT command is enough to write to ROM at address 0.

El voilà Danjovic, the full article!
It is in Portuguese, but it is not difficult to understand.
To switch the display from normal to inverse, it is used POKE 65500.

Greetings.

PokeMon wrote:

Paul wrote:Be aware that the first five bytes of the rom are being written to by the floating point routines of the rom.

Not only floating point, a simple PRINT command is enough to write to ROM at address 0.

Uh oh, I didn't knew that. I am not so used in ZX81 architecture... Thanks for the advice! I'll try another address doing Sinclair way, I mean, using as few chips as possible.

[]s
Daniel

user@lab1 wrote:El voilà Danjovic, the full article!
It is in Portuguese, but it is not difficult to understand.
To switch the display from normal to inverse, it is used POKE 65500.

Greetings.

Thanks! Portuguese is my mother language . I am from Brasil!

I think that the circuit can be enhanced by the use of a 74LS138 for decoding. While keeping /WR and /MREQ at /G2A and /G2B and A15 in G1 I have then 8 options for addresses at each 4K above $8000 by attaching A14, A13 and A12 at the A,B,C inputs of the '138. A wise choice would avoid problems of interoperability with peripherals like ZXpand . I'll think about it...

[]s
Daniel