IBM RT Series Hardware Reference Manual page 208

Register Mode of Operation
Name Port Index 0 1 2 3 4 5 6 7 0 E F 10 F! 10: 0* 1* 2* 3*
Palette
3CO OC
14 14 14 14 14 14 17 18 14 14 00 04 00 3C 3C 3C 3C 3C
Palette
3CO
OD 15 15 15 15 15 15 17 18 15 15 18 07 18 3D 3D 3D 3D 3D
Palette
3CO OE
16 16 16 16 16 16 17 18 16 16 00 00 00 3E 3E 3E 3E 3E
Palette
3CO
OF 17 17 17 17 17 17 18 17 17 00 00 00 3F 3F 3F 3F 3F 3F
Mode Control 3CO 10 08 08 08 08 01 01 01 OE 01 01 OB OB OB 01 08 08 08 08
Overscan
3CO
11 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Color Plane
3CO 12 OF OF OF OF 03 03 01 OF OF OF 05 05 05 OF OF OF OF OF
Hrz Panning
3CO
13 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
·Values for these modes when the IBM Enhanced Color Display is attached
:Values for these modes when greater than 64K Graphics Memory is installed
Attribute Registers (2 of 2)
68 IBM Enhanced Graphics Adapter