$02A6/678:	TV Standard: $00 = NTSC, $01 = PAL

At power-on, a test is performed to see if the monitor uses the NTSC (North American) or PAL (European) television standard.

This test is accomplished by setting a raster interrupt for scan line 311, and testing if the interrupt occurs. Since NTSC
monitors have only 262 raster scan lines per screen, the interrupt will occur only if a PAL monitor is used. The results of that
test are stored here, with a 0 indicating an NTSC system in use, and one signifying a PAL system.

This information is used by the routines which set the prescaler values for the system IRQ timer, so that the IRQ occurs every
1/60 second. Since the PAL system 02 clock runs a bit slower than the NTSC version, this prescaler value must be adjusted
accordingly.

Kernal-Reference:

 LDA $02A6   : $F42C $FDDD
 STA $02A6   : $FF68

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