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Magnus Clyde

The exact speed of the TIA

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The Atari 2600 main clock is 3.58 mhz which is fed to the TIA chip.  The TIA chip divides this by 3 to provide the CPU clock running at 1.19mhz.

 

3.58 mhz is the frequency used by the NTSC color sub-carrier.

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I mean, how precise do you want it? This is the Phi0 clock signal being fed into SALLY on a 7800 while playing a 2600 game:

 

1040234782_CPUPhi02600Game.thumb.png.48cba965ef1c26db5c4409ce52383983.png

 

And this is the OSC input to the TIA from the NTSC crystal on the board:

 

956485994_TIAOSC7800Game.thumb.png.52588fc83726f33ad4d8b5ad2feded13.png

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20 minutes ago, ClausB said:

1,193,182 Hz

I understand there are slight differences between PAL/NTSC/SECAM but I don't know the exact figures.

 

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NTSC
TIA CLOCK    =     3579545 Hz
CPU CLOCK    =    1193182 Hz

 

PAL
TIA CLOCK     =    3546894 Hz    
CPU CLOCK    =    1182298 Hz

 

SECAM
TIA CLOCK    =    3562500    Hz
CPU CLOCK    =    1187500    Hz
 

PAL-M
TIA CLOCK    =     3575611 Hz
CPU CLOCK    =    1191870 Hz
 

 

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