Video Timing Register

Number	$11
Readable	Yes
Writable	Yes
Short Description	Sets video output timing variant.

(writable in config mode only)

Bit	Function
7-3	Reserved, must be 0
2-0	video signal timing variant

Possible timing variants:

Bit pattern	selected variant
%000	Base VGA timing, clk28 = 28000000
%001	VGA setting 1, clk28 = 28571429
%010	VGA setting 2, clk28 = 29464286
%011	VGA setting 3, clk28 = 30000000
%100	VGA setting 4, clk28 = 31000000
%101	VGA setting 5, clk28 = 32000000
%110	VGA setting 6, clk28 = 33000000
%111	HDMI, clk28 = 27000000

Each VGA setting increases the frequency by approximately 1 kHz. Experimental results based on what one vga monitor reports:

mode	50hz	60hz
vga0	49.3	58.1
vga1	50.3	59.3
vga2	51.9	61.1
vga3	52.8	62.2
vga4	54.6	64.3
vga5	56.4	66.4
vga6	58.1	68.5

50/60Hz depending on bit 2 of Peripheral 1 Register ($05).