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 Unpublished work Copyright 2000 Charles MacDonald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.