I feel sorry for the French too ... but

[I feel sorry for the French too ... but]

First, thanks to ChildOfCv for his astounding work on the French SECAM 2600 PCB/schematic

 

 

The  VCS was a dream when I was young, but it was for others ... we did not have TV at home (my parents choice) so my first Atari was an STE years later.

Now I'm old so I could get my dreams

 

I've got a SECAM 2600 but was barely knowing its specificity : only 8 (artificial) colors and more than 60% of the surface covered by the electronics dedicated to the BW to 8 SECAM color encoding with discrete logic.

 

I'm from the digital electronic age, so it took me time to dig into the old analog standards.

Here is a resume of my findings that I did not find in a single place:

 

NTSC TIA/NTSC console use only one crystal because TIA and the 2600 where completely designed for NTSC.

All is designed around the 3.579545 MHz frequency which is the NTSC color burst frequency/sub-carrier.

With a divide by 3, TIA provide the CPU clock : 1.193181MHZ

And on NTSC, the color sub-carrier is defined as 455/2 x line rate(15.734 Khz), witch permit line (and pixels for the TIA) frequency generation with cascaded integer dividers (5x7x13).

TIA has an horizontal resolution of 228 color clock (blanking included)

Clearly you could see that 455/2=227.5 ~ 228 the pixel clock = color sub-carrier frequency = main crystal

On the 2600, frame rate/line per frame is controlled in software by the CPU at TIA ticks (sync between the TIA and the CPU)

 

Next come the PAL TIA/Console.

The PAL system has a color sub-carrier frequency of 4.43361875MHZ

The color sub-carrier is defined as 283.75 colour clock cycles per line plus a 25 Hz offset to avoid interferences  : 283.75 × 15228625 Hz + 25 Hz

We could see that the pal colour cycles are ~5/4 of 228 TIA standard pixels clock per line.

 

So what is a PAL TIA ?

This is simply a NTSC TIA (Luma generation is exactly the same) with an external pin for the oscillator for the chroma generator as we could no longer use the main oscillator and a minor adaptation on the  chroma generator for the pal color encoding (a 180° color signal phase rotation on each line). As the oscillator is now external, we have the pal-S/900khz-out pin too to drive it.

To match the TIA 228 color pixel clock per line we need to respect a 5/4 ratio between the main TIA clock and the color generator clock.

We get:

4.433618MHZ => crystal for the pal color generator

4.433618MHZ * 4/5 => 3.546894MHZ => main crystal of the TIA

3.546894MHZ/3 => 1.182298MHZ=> CPU clock

 

And what is a SECAM 2600 ?

Well, looking at the schematic from ChildOfCv, we see that the TIA is only used for luma generation.

8 Secam Chroma mapped on the 8 luma values.

The secam chroma generator use a 4.453125Mhz crystal witch is still driven by the 900khz output => pal/secam/ntsc sync and color sync logic is the same or mostly compatible (At the TV, not for on the air RF....)

Remark here: as the NTSC TIA does not have the 900khz output, another trick is surely used on first SECAM models (pin 6 BLK* ?)

With the applied previous logic, to respect the 4/5 ratio, main TIA crystal should be 3.5625Mhz Bingo ! it is !
And the CPU clock is 1.1875MHZ, slower than NTSC console but faster than PAL ones !

 

For 2600 SECAM model to PAL conversion we need to (it was my first motivation):

- rewire the BW/Color switch to the CPU => on the SECAM version, the swich drive the SECAM color generator, and the cpu bw/color info pin is grounded.

- feed the pin 8 with the output of the 4.453125Mhz Oscillator (r278/r2800/q208) which is exactly the same as the PAL one.

- change the two crystals (I suspect that it should work too without the change).

- add the 1k pullup to the col signal

- add the color adjustment circuit with the voltage elevator on the osc (as the original 2600(not A) NTSC or PAL version)  : one pot, two diodes and tree caps.

=> now you could add a s-video/composite mod like the UAV and voila.

 

The more interesting part :

With the Tim Worthington RGB mod and a modern programmable clock generator plugged in place of the crystals you could have a true multi-standard 2600, with RGB/PAL or NTSC s-video and composite, at PAL/NTSC or SECAM CPU speed (will need some adjustments on the RGB board). For the sake of preservation, add a few gates to rewire on the fly the console in PAL or SECAM and add a 8 color SECAM RGB out.

A single board to do it will be a future project.

Will report here if something work/progress.

 

[Super Game Module - French SCART version]

Hello,

Is the expansion port pinout difference between CV scart models and others documented somewhere ?

[I feel sorry for the French...]

👍

Thank you

[Vectrex SD Cart?]

Hello Richard

You could put me on the list too for a VectMulti when ready.

Thank you for your hard work.

[I feel sorry for the French...]

France get standard Pal 7800 with integrated RGB converter as an addon card (not a verry good one for today standards) and without the modulator.

There is some pictures in the 7800 topics.

[Where to buy homebrew]

Great ! Thank you !

[Where to buy homebrew]

Any new site to buy Kristof games ?

http://kristofsnewvectrexgames.comli.com site is definitively down.

[AtariVox+ Few oddities]

Instead of simply lifting pin14 of the PIC, did you tried to ground pin14 ?

It will kill all back powering.

But it could be not sufficient to "fix" the problem. If there is some internal leak capable of back powering the chip, the leak could be one source of the speakjet disturbing.

It's worth a try.

If it does not fix the problem, we should get the complete schematic and with the datasheet and errata of the pic chip find witch pin need proper additional care / signal conditioning under no power condition to not disturb the connected signal.

[sd cartridge for 7800?]

1.79Mhz is not very fast. 550ns is plenty of time in today standards and old rom are slow too, more than 120ns access time for sure.

Faster imply more power too. So power consumption is still the more probable track. We will see.

Even if the compatibility is way better with theses memory chips and confirm power supply exhaustion with the first ones, the most affected 7800 units will still need a regulator/power supply refresh (and perhaps decoupling capacitors refresh/enhancement).

[sd cartridge for 7800?]

And 12v are about 15v~18v without load too.

Will see as TO220 is 50°C/Watt junction to air and 7805 max junction temps is 125°C.

You could use tree or four 1N400x in series to drop the voltage if you have that in your drawer.

[sd cartridge for 7800?]

I have a 12vdc power supply that is 1.25A. I will build a converter to plug it into the Atari 7800 and test if my results are better tonight.

Be careful, at 1A it will be 3 more watts of heat to be dissipated by the internal 7805 than with the 9vdc power supply.

It could be as bad as a flaky 9v power supply.

[sd cartridge for 7800?]

As most have video modded 7800, I think that a regulator and PSU modding is a must for them.

I suspect that even with original cartridges these same units to a leaser extend exhibits some incompatibilities.

In this case, trying to fully solve the problem on the Concertos side could be a dead end.

Wall mounted 9V 2A or more are cheap today. And for those which not want to do heavy internal power mod, a correctly cooled modern low noise 7805 could go up to 1.5A (ST L7805ACV-DG or L7805ABV-DG).

7805 are near indestructible but goes down/oscillate when entering thermal/power overload.