Programming Considerations - IBM RT Series Hardware Reference Manual

Programming Considerations
The following table summarizes the 6845 controller module's
internal data registers, their functions, and their parameters. For
the IBM Monochrome Display, the values must be programmed
into the 6845 to ensure proper initialization of the display.
IBM Monochrome
Register Register Program Display
Number File Unit (Address in hex)
RO Horizontal Total Characters 61
R1 Horizontal Displayed Characters
50
R2 Horizontal Sync Position Characters 52
R3 Horizontal Sync Width Characters F
R4 Vertical Total Character Rows 19
R5 Vertical Total Adjust Scan Line 6
R6 Vertical Displayed Character Row 19
R7 Vertical Sync Position Character Row 19
R8 Interlace Mode
---------
02
R9 Maximum Scan Line Scan Line D
Address
R10 Cursor Start Scan Line B
R11 Cursor End Scan Line C
R12 Start Address (H)
_
....
_------
00
R13 Start Address (L) --------- 00
R14 Cursor (H)
---------
00
R15 Cursor (L)
---------
00
R16 Reserved --------- --
R17
Reserved
---------
--
To ensure proper initialization, the first command issued to the
IBM Monochrome Display and Printer Adapter must be sent to
the CRT control port 1 (hex 3B8), and must be a hex 01, to set
the high-resolution mode. If this bit is not set, the system unit's
microprocessor's access to the adapter must never occur.
If
the
high-resolution bit is not set, the system unit's microprocessor will
stop running.
System configurations that have both an IBM Monochrome
Display and Printer Adapter, and an IBM Color/Graphics
Monitor Adapter, must ensure that both adapters are properly
initialized after a power-on reset. Damage to either display may
occur if not properly initialized.
Monochrome Adapter 5