Programming Considerations; Programming The 6845 Crt Controller; Sequence Of Events; Memory Requirements - IBM 5150 Hardware Reference Manual

Programming Considerations
Programming the 6845 CRT Controller
The following table summarizes the 6845 Internal Data Registers and
their functions and parameters. For the IBM Monochrome Display,
r--..,
the values in the table must be programmed into the 6845 to insure
proper initialization of the device.
Table 2. 6845 INITIALIZATION PARAMETERS
REGISTER REGISTER
PROGRAM 80x25
# FILE
UNIT MONOCHROME
RO
HORIZONTAL TOTAL
CHARACTERS 61H
Rl
HORIZONTAL OISPLAYED CHARACTERS
50H
R2
HSYNC POSITION CHARACTERS 52H
R3
HSYNC WIDTH CHARACTERS FH
R4 VERTICAL TOTAL
CHAR ROWS 19H
R5
VTOTAL ADJUST SCAN LINE
6H
R6 VERTICAL DISPLAYED
CHAR ROW 19H
R7 VSYNC POSITION CHAR ROW
19H
RS INTERLACE MODE
- - -
02
R9
MAX SCAN LINE ADDRESS SCAN LINE
DH
R10 CURSOR START
SCAN LINE
BH
Rll CURSOR END SCAN LINE CH
R12
START ADDRESS (H)
---
DOH
R13 START ADDRESS
(L)
---
DOH
R14
CURSOR (H)
---
DOH
R15
CURSOR
(L)
- - -
DOH
R16 RESERVED
---
- - ­
R17 RESERVED
---
--­
Sequence of Events
The first command issued to this attachment must be to output to
PORT 3B8, hex 01, to set high resolution mode. If the high resolution
mode is not set, an infinite CPU wait-state will occur!
Memory Requirements
The attachment has 4K bytes of memory which is used for the display
buffer. The memory supports one screen of 25 rows of 80 characters,
plus a character attribute for each display character. No parity is
provided on the memory. No system Read/Write memory is required
for the monochrome adapter portion. The display buffer starts at
address 'BOOOO'.
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