TIA to VHF module interface (SECAM 2600)

[Windless]

Hi,

 

  I try to understand how the TIA is connected to the VHF module on a SECAM 2600, having in mind to try displaying the proper colors instead of the 8 ugly ones.

 

  From what I've found for now, LUM0/1/2 behave exactly as expected from the TIA (no difference on LUMx on NTSC and PAL TIAs). Now the problem is the color signal :

-Is there a document about how the color is encoded on either PAL or NTSC TIA ?

-I've read somewhere on this forum that you can get the signal from the COL pin of a TIA on a SECAM 2600 because it's missing a clock signal hence it won't produce the output, but no precise information.

 

  Do you know where to find any of these information ?

 

Thanks,

Windless.

[Windless]

Digging the forum :

 

-In mid 2015, alex_79 gives some hints about how the TIA has some pin (which one ?) set to ground for PAL, NTSC, and W&B switched SECAM, and LUMx are used as RVB on color mode SECAM. Also refers to a lacking "additional oscillator circuit needed to generate the PAL chroma signal",I'll try to find in schematic where this is (inside the modulator or connected to the TIA ? If it is inside the modulator, it seems possible to read the LUMx and COL from the TIA and use them in either a scavenger or home made modulator ? Or an high frequency IC which could output VGA / HDMI signal ?)

 

 

-In late 2015,Apocalypse had something similar in mind but the topic ended without a real conclusion.

 

Edited July 14, 2019 by Windless

[alex_79]

On 7/14/2019 at 5:56 PM, Windless said:

-In mid 2015, alex_79 gives some hints about how the TIA has some pin (which one ?) set to ground

The grounded pin I was referring to in that old thread is on the 6532 RIOT chip, not TIA.

On NTSC and PAL consoles, pin 21 of the 6532 is wired to the "TV TYPE" switch, which grounds the pin when in B&W position, while leaves it floating in "COLOR" position.

The status of the pin can be read by the console and early games used it to select a palette optimized for B&W Televisions, while later games either ignored it or used it for other purposes.

 

On a SECAM console that pin is grounded and not connected to the TV TYPE switch (that switch on SECAM consoles actually disables the color generation and its status cannot be read by the software).

Therefore PAL and NTSC games played on a SECAM consoles will always "see" the TV TYPE switch as if it's in B&W position.

 

On 7/14/2019 at 5:56 PM, Windless said:

Also refers to a lacking "additional oscillator circuit needed to generate the PAL chroma signal",I'll try to find in schematic where this is (inside the modulator or connected to the TIA ?

Connected to the TIA: