IBM RT Series Hardware Reference Manual page 183

Bit 6
CRTC Out Pin
MA O/RFA 0
MA 1/RFA 1
MA 2/RFA 2
MA 3/RFA 3
*
*
*
MA 14/RS 3
MA 15/RS 4
Bit 7
Word Mode or Byte Mode-When this bit is a
logical 0, the Word Mode shifts all memory
address counter bits down one bit, and the most
significant bit of the counter appears on the least
significant bit of the memory address outputs.
See table below for address outPQt details. A
logical 1 selects the Byte Address mode.
Internal Memory Address Counter
Wiring to the Output Multiplexer
Byte Address
Word Address
Mode Mode
MAO MA 15 or MA 13
MA1 MAO
MA2 MA1
MA3
MA2
* *
* *
* *
MA14 MA13
MA15 MA14
Hardware Reset-A logical 0 forces horizontal
and vertical retrace to clear. A logical 1 forces
horizontal and vertical retrace to be enabled.
Line Compare Register
This is a write-only register pointed to when the value in the CRT
Controller address register is hex 18. The processor output port
address for this register is hex 3B5 or hex 3D5.
Line Compare Register Format
Bit 7 6 5 4 3 2 1 0
Bit O-Bit 7
I I I I I I I
Line Compare Target
Line Compare-This register is the low-order 8
bits of the compare target. When the vertical
IBM Enhanced Graphics Adapter 43