Registers - IBM RT Series Hardware Reference Manual

Registers
External Registers
This section contains descriptions of the registers of the Enhanced
Graphics Adapter that are not contained in an LSI device.
Name Port Index
Miscellaneous Output Register 3C2
-
Feature Control Register
3?A
-
I nput Status Register 0
3C2
-
Input Status Register 1
3?2
-
?
=
B in Monochrome Modes ?
=
Din Color Modes
Miscellaneous Output Register
This is a write-only register. The processor output port address is
hex 3C2. A hardware reset causes all bits to reset to zero.
Miscellaneous Output Register Format
Bit 7 6 5 4 3 2 1 0
Bit 0
I/O Address Select
Enable Ram
Clock Select 0
' - - - - - - - - - J ..
~ Clock Select 1
Disable Internal Video Drivers
Page Bit For Odd/Even
Horizontal Retrace Polarity
& . . . . - - -_ _ _ _ _ _ _
~
Vertical Retrace Polarity
3BX/3DX CRTC I/O Address-This bit maps
the CRTC I/O addresses for IBM Monochrome
or Color/Graphics Monitor Adapter emulation.
A logical 0 sets CRTC addresses to 3BX and
Input Status Register 1 's address to 3BA for
Monochrome emulation. A logical 1 sets CRTC
12 IBM Enhanced Graphics Adapter