Standard Display Controller Registers (PC CGA/MDA Compatible)
I/O Address Bits R/W Mode Description
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03B4h/03D4h 4-0 R/W CRTC index - MDA/CGA CTRC index register
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03B5h/03D5h CRTC data - Indexed MDA/CGA CTRC data registers
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-0Ah CurStart - cursor start scan line and blink mode
6-5 R/W CurBlinkBits - cursor blink mode
4-0 R/W CurStartBits - cursor start scan line
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-0Bh 4-0 R/W CurStop - cursor stop scan line
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-0Ch 5-0 R/W DspStHi - display start address high
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-0Dh 7-0 R/W DspStLo - display start address low
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-0Eh 5-0 R/W CurLocHi - cursor location high
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-0Fh 7-0 R/W CurLocLo - cursor location low
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-10h 5-0 R LpenHi - Light pen high; reads same as cursor address high
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-11h 7-0 R LpenLo - Light pen low; reads same as cursor address low
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03B8h/03D8h Mode - MDA/CGA mode control register
6 R/W EnUndl - enable underline character attribute
5 R/W EnBlink - enable blink character attribute
4 R/W HiResGr - enable high resolution graphics
3 R/W Unblank - unblank display
2 R/W AlphaBW - disable alpha color
1 R/W Graphics - 1=graphics, 0=alpha
0 R/W HiResText - enable high resolution alpha
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03D9h - - Palette - CGA palette register (not implemented)
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03BAh/03DAh Status - MDA/CGA status register
3 R Vsync - vertical sync
2 R LPswitch - light pen switch
1 R LPS - light pen status
0 R Hsync - horizontal sync
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03DBh - - ClrLPS - clear LPS bit in status register
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03DCh - - SetLPS - set LPS bit in status register
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