=== Overscan bits ===
Details about Reg. It's possible to use 32KB screen size (used for [[Programming:Overscan|overscan]]) by setting bits 11 and 10 of Register 12 both to 1. Bits MA11 and RegMA10 of the address generated by the CRTC are not written on the address bus to access video memory; settings both bits to 1 is the only way to cause a carry to bit MA12 when address pass over the end of current video page to change the memory address to the next video page. 13 specifically:
.------- REG 12 --------. .------- REG 13 --------.
| 1| 1| 32Ko | | 1| 1| C000 - FFFF |
'--'--'--------------' '--'--'---------------'
So, it's possible to use 32KB screen size (used for [[Programming:Overscan|overscan]]) by setting bits 11 and 10 both to 1 (of Register 12). Bits MA11 and MA10 of the address generated by the CRTC are not written on the address bus to access video memory; settings both bits to 1 is the only way to cause a carry to bit MA12 when address pass over the end of current video page to change the memory address to the next video page.
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