mirror of
https://github.com/ekeeke/Genesis-Plus-GX.git
synced 2024-11-12 22:05:06 +01:00
41 lines
1.4 KiB
Plaintext
41 lines
1.4 KiB
Plaintext
|
|
VDP timing for an NTSC Genesis in display mode 5.
|
|
Version 0.4 (11/29/00)
|
|
|
|
by Charles MacDonald
|
|
WWW: http://cgfm2.emuviews.com
|
|
|
|
Unpublished work Copyright 2000 Charles MacDonald
|
|
|
|
Description 32-cell 40-cell
|
|
----------------------------------------------------------------------------
|
|
Range 00-93, E9-FF 00-B6, E4-FF
|
|
Display area 00-7F 00-9F
|
|
V counter increment 84, 85 A4, A5
|
|
V-blanking in 86, 87 A7, A8
|
|
V-blanking out 86, 87 A7, A8
|
|
H-blanking in 93, E9 B2, E4
|
|
H-blanking out 06, 07 06, 07
|
|
|
|
Comma seperated values show the H counter value before an event occurs,
|
|
and then the H counter value immediately after.
|
|
|
|
These values shouldn't be considered 100% accurate, they are probably
|
|
off by one or two.
|
|
|
|
Each H counter unit is equivalent to two pixels.
|
|
|
|
The gaps at 93-E9 and B6-E4 are where the H counter 'jumps' ahead.
|
|
The H counter will never actually be set to the values 94-E8 or B7-E3.
|
|
Perhaps this is the horizontal retrace period.
|
|
|
|
Interestingly enough, the timing values for the 32-cell display mode
|
|
are identical to that of the SMS.
|
|
|
|
It would appear that in 40-cell mode, the horizontal blanking period
|
|
is shorter as the active display period takes more time.
|
|
|
|
The V-blanking flag can also be forcibly set by disabling the display
|
|
through bit 6 of register #1.
|
|
|