PCW 8256 in colour, cheap and easy

[squelch41]

I'm struggling to get this working properly -

I get video fine from the pico but if I run anything with grey scales eg head over heels, I cant see anything other than the bright white text. In the game, I can see the play character but not the lives or the pattern on the floor.

This is the same for any of the colour modes.

I've use 270ohm resistors on RGB, 1k on sync and 100ohm on RGB blanking.

Even if I bypass the resistors, the problem remains.

What am I doing wrong?

Hard to diagnose remotely, I would check first if you are getting voltages from all R G B pins on the pico. Display something with all white pixels on the screen and check voltages on the pico output pins. But if you are getting white text I would expect it to work.

Also in normal 2 colour mode boot to cpm and see if text is green, then and try connecting G output from pico to R input on your RGB lead, see if you are getting red text, and try the same with B input as well to see if the text is blue. This should test all 3 channels.

Thanks - I'm getting red, green and blue output and the mode switch works.
When I 'scope the pins I get quite low voltages -
This is without anything connected to the pico, just the values after the resistors:

(Yellow is the green channel, blue is the sync pin - all taken on the head over heels start screen)






With the scart connected to a monitor, I get



I thought that if I bypassed the resistors, that might help but it doesnt make any difference.

This is the Head over Heels start screen as a photo of the monitor:

[fuzzweed]

Silly question. Is it rgb capable monitor? Scart =/= rgb

[squelch41]

Silly question. Is it rgb capable monitor? Scart =/= rgb

Hehe, yes  
Tried on my SCART scaler that I use for megadrive, snes etc with RGB scart cables and a Sony LCD TV which has a couple of other rgb scarted consoles 

[eto]

Silly question. Is it rgb capable monitor? Scart =/= rgb

Hehe, yes
Tried on my SCART scaler that I use for megadrive, snes etc with RGB scart cables and a Sony LCD TV which has a couple of other rgb scarted consoles

Does the cable you use with the PCW have a voltage on the RGB detect pin? 

That's a common issue on the CPC that the TVs don't switch to RGB mode.

[fuzzweed]

You can bluff that with a battery. Put 1.5v on pin 16 should do it

[squelch41]

Silly question. Is it rgb capable monitor? Scart =/= rgb

Hehe, yes
Tried on my SCART scaler that I use for megadrive, snes etc with RGB scart cables and a Sony LCD TV which has a couple of other rgb scarted consoles

Does the cable you use with the PCW have a voltage on the RGB detect pin?

That's a common issue on the CPC that the TVs don't switch to RGB mode.

Yes, it's in the schematic - 3.3v taken from the pico at pin 36.

I'm getting RGB as all the colours are visible - it just seems to either not be sampling the pcw signal correctly (so detecting the grays as black) or not outputting a strong enough signal to the scart (so essentially it is compressing down the levels) but I'm not sure which. 

Or, it's something else that I am missing as a novice with analog video 

[fuzzweed]

Could that be over voltage? Just googling / guessing here, but rgb select says 1-3v