Region Switching (Master System 2)
The region on a Master System 2 is controlled via the 315-5246 VDP (Video Display Processor), often it is labelled IC5 and below the cartridge port, and the CXA1145 (Video Encoder).
Changing the region changes the output frequency between 50Hz for PAL, and 60Hz for NTSC.
Pin 57 of the 315-5246 is the PAL/!NTSC pin, meaning at 5V it would be PAL and at 0V it would be NTSC.
The VDP internally pulls the pin high, so you could cut it free to be in PAL mode, and drive it to ground for NTSC, via a switch.
Here is an example of converting a PAL Master System 2 to 60Hz by cutting, lifting and sending pin 57 of the 315-5246 to ground.
The CXA1145 has been left as this is an RGB modded console.
Changing this pin will change the region of the console, however the CXA1145 (the video encoder that generates composite/RGB) will also need changing. The CXA1145 has its pin 5 which is the inverse of the VPD. At 5V it would be NTSC, and at 0V it would be PAL.
Therefore, if you wanted to change the region and also update the chroma colors on composite to be the correct frequency to match the region, you must set the pin 5 of the CXA1145 to the inverse of the pin 57 on the 315-5246.
If using RGB only, there is no need to change the CXA1145 pin as RGB does not have a chroma signal with specifical PAL/NTSC timings.
It is worth noting although the CXA1145 has a built-in sub-carrier chroma generator that changes from the PAL/NTSC pin setting to generate the right timings, the external delay bandpass filters on the chroma in (pin 17) and chroma out (pin 15) would be the wrong frequency so slightly wrong filtering.
PAL should use a 4.43MHz filter, and NTSC should use a 3.58MHz.
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