Commodore PC 40 - Page 59

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3ba: Status register (read only)
bit 0: horizontal sync
bit 1: unused
bit 2: unused
bit 3: video signal
bit 4: unused
bit 5: unused
bit 6: unused
bit 7: vertical sync
3ba: Mode
select register (write only)
bit 0: reserved
bit 1: unused
bit 2: unused
bit 3: 132-column text for monochrome
bit 4: 132-column text for color
(bit 0 of 3d8 must be 1)
bit 5: set emulation mode in lieu of DIP-Switch
bit 6: set mono mode in lieu of DIP-Switch
bit 7: set color mode in lieu of DIP-Switch
3bf:
(write only)
bit 0: 0 = disable setting of monochrome graphics mode
(3b8 bit 1)
1 = enable setting of monochrome graphics mode
(3b8 bit 1)
bit 1: 0 = disable setting of monochrome graphics page bit
(3b8 bit 7)
1 = enable setting of monochrome graphics page bit
(3b8 bit 7)
bit 2-7: unused
1/0 registers for:
IBM Color/Graphics adapter
Plantronics Color/Graphics adapter
Color 132-column text mode
Emulation mode
light pen
The following lists the lIO registers used in these modes:
3dO -
3dl: synonym for 3d4 - 3d5
3d2 - 3d3: synonym for 3d4 - 3d5
3d4: 6845 ClIT controller register address port
3d5: 6845 CRT controller register data port
Using ATI 43