First post, by vladstamate
- Rank
- Oldbie
I am trying to draw this for my simple understanding
[<---------------------------------------------->] HORIZ TOTAL 45
[<------------------->| ] HORIZ DISPLAY END 20
[ |<-->] HORIZ START/END BLANK 43->45
[ |<---------->] HORIZ START/END RETRACE 40->45
[000000000000000000000000000000000001111111111111] Bit 0 of the 3DA status word
[<---------------------------------------------->] VERTICAL TOTAL 364
[<----------------------------->| ] VERTICAL DISPLAY END 349
[ |<-------->| ] VERTICAL START/END BLANK 350->360
[ |<---------->| ] VERTICAL START/END RETRACE 351->362
[000000000000000000000000000000000111111111111111] Bit 0 of the 3DA status word
[000000000000000000000000000000000111111111111111] Bit 7 of the 3DA status word
So few questions:
1) Is my understanding correct about the bit 0 and 7 of the status word? As long as we are in either retrace they should be 1
2) What does horizontal/vertical blanking mean? How is that different than retrace? It seems to happen during the retrace timing? According to the EGA manual it is this. But I do not understand it.
"This register determines when the horizontal blanking output signal becomes active. The row scan address and underline scan line decode outputs are multiplexed on the memory address outputs and cursor outputs respectively during the blanking interval. These outputs are latched external to the CRT Controller with the falling edge of the BLANK output signal. The row scan address and underline signals remain on the output signals for one character count beyond the end of the blanking signal."
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