Programmer 7500/MAX_PROGRAMMERS.iso/PROGRAMS/UTILS/HARDWARE/LED_CRT.ZIP/LED-CRT.TXT

Text File | 1986-12-17 | 25.2 KB | 656 lines

     The following text was copied from a photocopy distributed by Leading
Edge Hardware Products.  It contained no copyright notice, and I can't
imagine the LE would care that I reproduced it.  They'll send it to you free
if you ask them for it.  I have proof-read this document very carefully, but
gremlins may have crept in.  Use the information contained herein at your
own risk.

                The Model "D" Video Controller

     The Model "D" video controller has the combined capability of the IBM
Monochrome Display Board and the IBM Color Graphics Display Board.  It also
provides Hercules Compatible Monochrome Graphics and a High Resolution 640 X
200 16 color graphics mode.

     Since there is only one 6845 CRT controller chip used in the circuitry,
the system cannot run in both modes simultaneously.  The video mode switch in
the rear of the machine functions in two ways.  It physically changes the I/O
address of the CRT controller chip and related registers between MONOCHROME
(03BxH) and COLOR (03DxH) and is actually DIPswitch 2-5, which selects
monochrome or color mode at power on.

     There is 64K of video RAM associated with the controller and resides
from address B0000H to address BFFFFH.  This is used to hold the
characters/attributes or graphic dot patterns to be displayed on the screen.

     Below is a description of each of the modes and sample programs for
initializing the controller to be in each of the modes.  Throughout this
document bit 7 is the most significant bit and bit 0 is the least significant
bit.


*********************
*                   *
*  MONOCHROME MODE  *
*                   *
*********************

80 X 25 TEXT MODE

     In alphanumeric mode 80 columns by 25 rows of characters can be
displayed.  The characters are mapped into even locations from addresses
B0000H to B0FFFH.  The attributes are mapped into the odd locations.
Location B0000 corresponds to the top left corner of the screen.  The
attribute determines how the character is to be displayed.  The various
attributes are as follows:

            data bits
         7 6 5 4 3 2 1 0     hex         style of text
         ---------------     ---         -------------------
         0 0 0 0 0 0 0 0      00         no character display
         0 0 0 0 0 0 0 1      01         underlined character
         0 0 0 0 0 1 1 1      07         normal character
         0 0 0 0 1 0 0 1      09         underline, high intensity
         0 0 0 0 1 1 1 1      0F         high intensity character
         0 1 1 1 0 0 0 0      70         reverse video character
         1 0 0 0 0 0 0 1      81         blinking, underlined character
         1 0 0 0 0 1 1 1      87         blinking, normal character
         1 0 0 0 1 0 0 1      89         blinking, underline, high intensity
         1 1 1 1 0 0 0 0      F0         blinking, reverse bideo
         1 1 1 1 1 0 0 0      F8         blinking, reverse vieo, high intensity

     The attribute determines how the character is to be displayed.  The
attribute byte in the color mode is much different than it was in the
monochrome mode.  Each of the bits in the attribute byte areas follows:

        Data bit   7  =  BLINK CHARACTER
                   6  =  RED BACKGROUND
                   5  =  GREEN BACKGROUND
                   4  =  BLUE BACKGROUND
                   3  =  INTENSITY CHARACTER
                   2  =  RED CHARACTER
                   1  =  GREEN CHARACTER
                   0  =  BLUE CHARACTER

     By setting some bits on and some bits off, you can create colored
characters on a differently colored background.  Also you have the choice of
making the character blink or not.


720 X 348 GRAPHICS MODE

     In monochrome graphics mode there are two pages of 720 X 348 pixels.
Each data bit in each byte represents a pixel on the display.  Each scan line
consists of 90 bytes of memory.  The adjacent scan lines which appear in the
display are not mapped adjacently in the video memory.  Below is a
representation of how the memory is arranged in the monochrome graphic mode.

            PAGE 0                                  PAGE 1
          ------------                          ----------------

       +-----------------------+              +-----------------------+
B0000  |                       |       B8000  |                       |
       | SCAN LINES 0,4,8 ETC  |              | SCAN LINES 0,4,8 ETC  |
       |                       |              |                       |
B1FFF  |                       |       B9FFF  |                       |
       +-----------------------+              +-----------------------+
B2000  |                       |       BA000  |                       |
       | SCAN LINES 1,5,9 ETC  |              | SCAN LINES 1,5,9 ETC  |
       |                       |              |                       |
B3FFF  |                       |       BBFFF  |                       |
       +-----------------------+              +-----------------------+
B4000  |                       |       BC000  |                       |
       | SCAN LINES 2,6,10 ETC |              | SCAN LINES 2,6,10 ETC |
       |                       |              |                       |
B5FFF  |                       |       BDFFF  |                       |
       +-----------------------+              +-----------------------+
B6000  |                       |       BE000  |                       |
       | SCAN LINES 3,7,11 ETC |              | SCAN LINES 3,7,11 ETC |
       |                       |              |                       |
B7FFF  |                       |       BFFFF  |                       |
       +-----------------------+              +-----------------------+

The page selection is done in the Display Control Register.  This will be
explained in detail later.


With color graphics there are 3 separate and different modes available.

320 X 200 MEDIUM RESOLUTION GRAPHICS MODE

     Each pair of data bits represents a pixel on the display.  Therefore
pixel can have 1 of 4 colors as follows:

       data bit 7,6 = C1,C0 respectively for the 1st pixel
                5,4 = C1,C0 respectively for the 2nd pixel
                3,2 = C1,C0 respectively for the 3rd pixel
                1,0 = C1,C0 respectively for the 4th pixel

    C1     C0        color set 0  color set 1  color set 2  color set 3
-----------------|--------------|------------|------------|-------------
     0      0       -----------predetermined background color-----------
     0      1      green          lt. green    cyan         lt. cyan
     1      0      red            lt. red      magenta      lt. magenta
     1      1      brown          yellow       lt. gray     white

     The color set and background color are selected by writing the
appropriate value to the Color Mode Regsiter at location 03D9H.

        data bit    0 = blue background
                    1 = green background
                    2 = red background
                    3 = intensity background
                    4 = color set bit 0
                    5 = color set bit 1
                    6 =
                    7 =

     Each scan line consists of 80 bytes of memory.  The adjacent scan lines
which appear on the display are not mapped adjacently in the video memory.
Below is a representation of how the memory is arranged in 320 X 200 graphics
mode.

       +------------------------+
B8000  |                        |
       | SCAN LINES 0,2,4 ETC   |
       |                        |
B9FFF  |                        |
       +------------------------+
BA000  |                        |
       | SCAN LINES 1,3,5 ETC.  |
       |                        |
BBFFF  |                        |
       +------------------------+

640 X 200 HIGH RESOLUTION 2-COLOR GRAPHICS

     Each data bit represents a pixel on the display.  Therefore each pixel
can have 1 of two colors.  The background color is always black.  The
foreground color may be any 1 of 16 available colors.  It is chosen by
writing the appropriate value to the Color Mode Register at location 03D9H.

    data bit   0 = blue background
               1 = green background
               2 = red background
               3 = intensity background
               4 =
               5 =
               6 =
               7 =

     Each scan line consists of 80 bytes of memory.  The adjacent scan lines
which appear on the display are not mapped adjacently in the video memory.
Below is a representation of how the memory is arranged in the 640 X 200
2-color graphics mode.


       +------------------------+
B8000  |                        |
       | SCAN LINES 0,2,4 ETC   |
       |                        |
B9FFF  |                        |
       +------------------------+
BA000  |                        |
       | SCAN LINES 1,3,5 ETC.  |
       |                        |
BBFFF  |                        |
       +------------------------+


640 X 200 HIGH RESOLUTION 16-COLOR GRAPHICS

     Four separate data bits represent a pixel on the display.  Therefore
each pixel can have 1 of 16 colors.  The 4 bits are in different banks of
memory.  Each bank of memory corresponds to red, green, blue, and intensity.

     Each scan line consists of 320 bytes of memory.  The adjacent scan lines
which appear on the display are not mapped adjacently in the video memory.
Below is a representation of how the memory is arranged in 640 X 200 16-color
graphics mode.


            INTENSITY BANK                        BLUE BANK
       +-----------------------+              +-----------------------+
B0000  |                       |       B4000  |                       |
       | SCAN LINES 0,2,4 ETC  |              | SCAN LINES 0,2,4 ETC  |
       |                       |              |                       |
B1FFF  |                       |       B5FFF  |                       |
       +-----------------------+              +-----------------------+
B2000  |                       |       B6000  |                       |
       | SCAN LINES 1,3,5 ETC  |              | SCAN LINES 1,3,5 ETC  |
       |                       |              |                       |
B3FFF  |                       |       B7FFF  |                       |
       +-----------------------+              +-----------------------+

           GREEN BANK                              RED BANK
       +-----------------------+              +-----------------------+
B8000  |                       |       BC000  |                       |
       | SCAN LINES 0,2,4 ETC  |              | SCAN LINES 0,2,4 ETC  |
       |                       |              |                       |
B9FFF  |                       |       BDFFF  |                       |
       +-----------------------+              +-----------------------+
BA000  |                       |       BE000  |                       |
       | SCAN LINES 1,3,5 ETC  |              | SCAN LINES 1,3,5 ETC  |
       |                       |              |                       |
BBFFF  |                       |       BFFFF  |                       |
       +-----------------------+              +-----------------------+


                       VIDEO CONTROLLER REGISTERS

6845 CRT INDEX REGISTER (03D4H / 03B4H)
     You set this register equal to the number of the data register into
which you want to write.

6845 CRT DATA REGISTER  (03D5H / 03B5H)
     In conjunction with the index register, it is used to initialize the
6845 for proper mode of operation.

 INDEX               DATA REGISTER VALUE (HEX)
--------    -----------------------------------------
            40X25    80X25    80X25    COLOR    MONO
            COLOR    COLOR    MONO     GRAPH    GRAPH
            -----    -----    -----    -----    -----
   0         38       71       61       38      35    HORIZONTAL TOTAL
   1         28       50       50       28      2D    HORIZONTAL DISPLAYED
   2         2D       5A       52       2D      2E    HORIZ SYNC POSITION
   3         0A       0A       0F       0A      07    HORIZ SYNC WIDTH
   4         1F       1F       19       7F      5B    VERTICAL TOTAL
   5         06       06       06       06      02    VERT TOTAL ADJUST
   6         19       19       19       64      57    VERTICAL DISPLAYED
   7         1C       1C       19       70      57    VERTICAL SYNC POSITION
   8         02       02       02       02      02    INTERLACE MODE
   9         07       07       0D       01      03    MAX SCAN LINE
   A         06       06       0B       06      0B    CURSOR START SCAN LINE
   B         07       07       0C       07      0C    CURSOR END SCAN LINE
   C         00       00       00       00      00    BUFFER START ADDRESS (H)
   D         00       00       00       00      00    BUFFER START ADDRESS (L)
   E         00       00       00       00      00    CURSOR POSITION (H)
   F         00       00       00       00      00    CURSOR POSITION (L)

     Changing the last 2 registers will allow various pages in color text
mode to be utilized.  The appropriate values are as follows:

          80 column mode                 40 column mode
         ----------------                ---------------
           REG C    REG D                 REG C    REG D
           -----    -----                 -----    -----
PAGE 0      00       00           PAGE 0   00       00
PAGE 1      08       00           PAGE 1   04       00
PAGE 2      10       00           PAGE 2   08       00
PAGE 3      18       00           PAGE 3   0C       00
                                  PAGE 4   10       00
                                  PAGE 5   14       00
                                  PAGE 6   18       00
                                  PAGE 7   1C       00

DISPLAY CONTROL REGISTER (03D8H / 03B8H)
     Allows the mode of the controller to be programmed.

   data bit  0 ----  0 = 40X25 (color only)       1 = 80X25
             1 ----  0 = alphanumerics            1 = graphics
             2 ----  0 = color                    1 = black/white
             3 ----  0 = disable video            1 = enable video
             4 ----  0 = 320X200                  1 = 640X200
             5 ----  0 = disable blink            1 = enable blink
             6 ----
             7 ----  0 = page 0 (mono graph)      1 = page 1


COLOR MODE REGISTER (03D9H)
     Allows the default colors in graphics mode to be selected.  This was
described previously.

DISPLAY STATUS REGISTER (03DAH / 03BAH)
     Allows software reading of VIDEO SYNC LINES and light pen status.

      data bit   0 = + HORIZONTAL SYNC
                 1 = + LIGHT PEN STROBE
                 2 = - LIGHT PEN SWITCH
                 3 = + VERTICAL SYNC
                 4 =
                 5 =
                 6 =
                 7 = - HORIZONTAL SYNC

RESET LIGHT PEN LATCH (03DBH / 03BBH)

PRESET LIGHT PEN LATCH (03DCH / 03BCH)

EXTENDED COLOR MODE REGISTER (03DDH / 03BDH)
     Allows selection of 16-color mode and software switch for toggling mode
switch on back of machine

       data bit   0 =
                  1 = SOFTWARE SWITCH (COLOR/MONO)
                  2 =
                  3 = ENABLE 16-COLOR MODE
                  4 =
                  5 =
                  6 =
                  7 =

     When bit 1 is set to on, this has the same result as physically
switching the video mode switch on the rear of the machine.  Resetting this
bit again will undo the previous toggle.  Note, if this is used the
controller must be reinitialized for the new mode.  Remember also the
toggling the switch changes the I/O address for the controller.


**********************
*   EXAMPLE PROGRAMS *
**********************

     All of the programs will be written in BASIC simply for simplicity's
sake.  They can be converted to other languages very easily.  Because of the
slower execution speed of BASIC, some of the programs may take a while to
clear the video memory and complete execution.  Please be patient.

EXAMPLE 1:  SET CONTROLLER UP FOR MONOCHROME TEXT MODE

1 rem clear monochrome text page
2 CLS:KEY OFF
5 DEF SEG=&HB000
10 REM set display control register to the needed value
20 REM   data bit 0 --- 1=80x25
30 REM            1 --- 0=ALPHANUMERICS
40 REM            2 --- 0
50 REM            3 --- 1=ENABLE VIDEO
60 REM            4 --- 0
70 REM            5 --- 1=ENABLE BLINK
80 REM            6 --- 0
90 REM            7 --- 0
100 OUT &H3B8,&H29
110 REM then initialize 6845 crt controller data registers
120 FOR INDEX=0 to &HF
125 OUT &H3B4,INDEX
130 READ BYTE
140 OUT &H3B5,BYTE
145 NEXT INDEX
150 REM display one character of each attribute
151 FOR ADDR=0 TO 22 STEP 2
152 READ CHAR$:CHAR=ASC(CHAR$)
153 READ ATTR
154 POKE ADDR,CHAR
155 POKE ADDR+1,ATTR
156 NEXT ADDR
160 GOTO 160
165 REM these are the 6845 register values for this mode
170 DATA &H61,&H50,&H52,&H0F,&H19,&H06,&H19
180 DATA &H19,&H02,&H0D,&H0B,&H0C,&H00,&H00,&H00,&H00
185 REM these are the characters and attributes to display
190 DATA A,&H00,B,&H01,C,&H07,D,&H09,E,&H0F,F,&H70
200 DATA G,&H78,H,&H81,I,&H87,J,&H89,K,&HF0,L,&HF3


EXAMPLE 2:  SET CONTROLLER UP FOR MONGRAPHICS MODE AND USE PAGE 1 OF MEMORY

1 REM clear second page of monochrome graphic memory
2 KEY OFF:DEF SEG=&HB800:FOR ADDR=0 TO &H7FFF:POKE ADDR,0:NEXT ADDR
10 REM set display control register to the needed value
20 REM     DATA BIT 0 --- 0
30 REM              1 --- 1=GRAPHICS
40 REM              2 --- 0
50 REM              3 --- 1=ENABLE VIDEO
60 REM              4 --- 0
70 REM              5 --- 0
80 REM              6 --- 0
90 REM              7 --- 1=PAGE 1
100 OUT &H3B8,&H8A
110 REM then initialize 6845 crt controller data registers
120 FOR INDEX=0 TO &HF
125 OUT &H3B4,INDEX
130 READ BYTE
140 OUT &H3B5,BYTE
145 NEXT INDEX
150 REM draw scan lines 0,4,8 etc
151 STADR=0:DEF SEG=&HB800
152 FOR X=1 TO 45 STEP 2:ADDR=STADR
153 FOR T=0 TO X
154 POKE ADDR,&HFF
155 ADDR=ADDR+1
156 NEXT T
157 STADR=STADR+90:NEXT X
160 REM draw scan lines 1,5,9 etc
161 STADR=0:DEF SEG=&HBA00
162 FOR X=1 TO 45 STEP 2:ADDR=STADR
163 FOR T=0 TO X
164 POKE ADDR,&HFF
165 ADDR=ADDR+1
166 NEXT T
167 STADR=STADR+90:NEXT X
170 REM draw scan lines 2,6,10 etc
171 STADR=0:DEF SEG=&HBC00
172 FOR X=1 TO 45 STEP 2:ADDR=STADR
173 FOR T=0 TO X
174 POKE ADDR,&HFF
175 ADDR=ADDR+1
176 NEXT T
177 STADR=STADR+90:NEXT X
180 REM draw scan lines 3,7,11 etc
181 STADR=0:DEF SEG=&HBE00
182 FOR X=1 TO 45 STEP 2:ADDR=STADR
183 FOR T=0 TO X
184 POKE ADDR,&HFF
185 ADDR=ADDR+1
186 NEXT T
187 STADR=STADR+90:NEXT X
190 GOTO 190
200 DATA &H35,&H2D,&H2E,&H07,&H5B,&H02,&H57
210 DATA &H57,&H02,&H03,&H0B,&H0C,&H00,&H00,&H00,&H00


EXAMPLE 3:  SET CONTROLLER UP FOR COLOR 40 X 25 TEXT MODE
1 REM clear color text page
2 DEF SEG=&HB800:CLS:KEY OFF
10 REM  set display control register to the needed value
20 REM     DATA BIT 0 --- 0=40X25
30 REM              1 --- 0=ALPHANUMERICS
40 REM              2 --- 0
50 REM              3 --- 1=ENABLE VIDEO
60 REM              4 --- 0
70 REM              5 --- 1=ENABLE BLINK
80 REM              6 --- 0
90 REM              7 --- 0
100 OUT &H3D8,&H28
110 REM then initialize 6845 crt controller data registers
120 FOR INDEX=0 to &HF
125 OUT &H3D4,INDEX
130 READ BYTE
140 OUT &H3D5,BYTE
145 NEXT INDEX
150 REM display one character of each attribute
151 ATTR=0:FOR ADDR=0 TO 510 STEP 2
152 CHAR=ATTR
154 POKE ADDR,CHAR
155 POKE ADDR+1,ATTR
156 ATTR=ATTR+1:NEXT ADDR
160 GOTO 160
165 REM these are 6845 register values for this mode
170 DATA &H38,&H28,&H2D,&H0A,&H1F,&H06,&H19
180 DATA &H1C,&H02,&H07,&H06,&H07,&H00,&H00,&H00,&H00


EXAMPLE 4:  SET CONTROLLER UP FOR COLOR 80 X 25 TEXT MODE AND
            USE PAGE 2 OF MEMORY

1 REM clear color text display
2 DEF SEG=&HBA00:CLS:KEY OFF
10 REM  set display control register to the needed value
20 REM        DATA BIT 0 --- 1=80X25
30 REM                 1 --- 0=ALPHANUMERICS
40 REM                 2 --- 0
50 REM                 3 --- 1=ENABLE VIDEO
60 REM                 4 --- 0
70 REM                 5 --- 1=ENABLE BLINK
80 REM                 6 --- 0
90 REM                 7 --- 0
100 OUT &H3D8,&H29
110 REM then initialize the 6845 crt controller data registers
120 FOR INDEX=0 TO &HF
125 OUT &H3D4,INDEX
130 READ BYTE
140 OUT &H3D5,BYTE
145 NEXT INDEX
150 REM display one character of each attribute
151 ATTR=0:FOR ADDR=0 TO 510 STEP 2
152 CHAR=ATTR
154 POKE ADDR,CHAR
155 POKE ADDR+1,ATTR
156 ATTR=ATTR+1:NEXT ADDR
160 GOTO 160
165 REM these are the 6845 register values for this mode
170 DATA &H71,&H50,&H5A,&H0A,&H1F,&H06,&H19
180 DATA &H1C,&H02,&H07,&H06,&H07,&H10,&H00,&H00,&H00


EXAMPLE 5 :  SET CONTROLLER UP FOR 320 X 200 COLOR GRAPHICS MODE
               USE COLOR SET 3 AND BACKGROUND OF BROWN

1 REM clear all of color video memory
2 KEY OFF
3 DEF SEG=&HB800:FOR ADDR=0 TO &H3FFF:POKE ADDR,0:NEXT ADDR
5 REM  set color mode register
6 OUT &H3D9,&H26
10 REM   set display control register to the needed value
20 REM        DATA BIT 0 --- 0
30 REM                 1 --- 1=GRAPHICS
40 REM                 2 --- 0
50 REM                 3 --- 1=ENABLE VIDEO
60 REM                 4 --- 0=320 X 200
70 REM                 5 --- 0
80 REM                 6 --- 0
90 REM                 7 --- 0
100 OUT &H3D8,&H0A
110 REM  then initialize 6845 crt controller data registers
120 FOR INDEX=0 TO &HF
125 OUT &H3D4,INDEX
130 READ BYTE
140 OUT &H3D5,BYTE
145 NEXT INDEX
150 REM draw scan lines 0,2,4 etc
151 STADR=0
152 DEF SEG=&HB800:FOR X=1 TO 45 STEP 2:ADDR=STADR
153 FOR TO=0 TO X
154 POKE ADDR,&H0:POKE ADDR+1760,&H55:POKE ADDR+3520,&HAA:POKE ADDR+5280,&HFF
155 ADDR=ADDR+1
156 NEXT T
157 STADR=STADR+80:NEXT X
160 REM  draw scan lines 1,3,5 etc
161 STADR=0
162 DEF SEG=&HBA00:FOR X=1 TO 45 STEP 2:ADDR=STADR
163 FOR TO=0 TO X
164 POKE ADDR,&H0:POKE ADDR+1760,&H55:POKE ADDR+3520,&HAA:POKE ADDR+5280,&HFF
165 ADDR=ADDR+1
166 NEXT T
167 STADR=STADR+80:NEXT X
190 GOTO 190
195 REM  these are the 6845 register values for this mode
200 DATA &H38,&H28,&H2D,&H0A,&H7F,&H06,&H64
210 DATA &H70,&H02,&H01,&H06,&H07,&H00,&H00,&H00,&H00


EXAMPLE 6:  SET CONTROLLER UP FOR 640 X 200 2-COLOR GRPAHICS MODE
                  AND USE FOREGROUND COLOR OF LIGHT MAGENTA

1 REM clear all of color video memory
2 KEY OFF
3 DEF SEG=&HB800:FOR ADDR=0 TO &H3FFF:POKE ADDR,0:NEXT ADDR
5 REM  set color mode register
6 OUT &H3D9,&HD
10 REM   set display control register to the needed value
20 REM        DATA BIT 0 --- 0
30 REM                 1 --- 1=GRAPHICS
40 REM                 2 --- 1=BLACK/WHITE
50 REM                 3 --- 1=ENABLE VIDEO
60 REM                 4 --- 1=640 X 200
70 REM                 5 --- 0
80 REM                 6 --- 0
90 REM                 7 --- 0
100 OUT &H3D8,&H1E
110 REM  then initialize 6845 crt controller data registers
120 FOR INDEX=0 TO &HF
125 OUT &H3D4,INDEX
130 READ BYTE
140 OUT &H3D5,BYTE
145 NEXT INDEX
150 REM draw scan lines 0,2,4 etc
151 STADR=0
152 DEF SEG=&HB800:FOR X=1 TO 45 STEP 2:ADDR=STADR
153 FOR TO=0 TO X
154 POKE ADDR,&HFF
155 ADDR=ADDR+1
156 NEXT T
157 STADR=STADR+80:NEXT X
160 REM  draw scan lines 1,3,5 etc
161 STADR=0
162 DEF SEG=&HBA00:FOR X=1 TO 45 STEP 2:ADDR=STADR
163 FOR T=0 TO X
164 POKE ADDR,&HFF
165 ADDR=ADDR+1
166 NEXT T
167 STADR=STADR+80:NEXT X
190 GOTO 190
195 REM  these are the 6845 register values for this mode
200 DATA &H38,&H28,&H2D,&H0A,&H7F,&H06,&H64
210 DATA &H70,&H02,&H01,&H06,&H07,&H00,&H00,&H00,&H00


EXAMPLE 7:  SET CONTROLLER UP FOR 640 X 200 16-COLOR GRAPHICS MODE
1 REM  clear all of video memory
2 KEY OFF
3 DEF SEG=&HB000:FOR ADDR=0 TO 65535!:POKE ADDR,0:NEXT ADDR
5 REM  set extended mode register
6 OUT &H3DD,&H8
7 REM  set border color to white
8 OUT &H3D9,0
10 REM   SET DISPLAY CONTROL REGISTER TO THE NEEDED VALUE
20 REM       DATA BIT 0 --- 0
30 REM                1 --- 1=GRAPHICS
40 REM                2 --- 0=COLOR
50 REM                3 --- 1=ENABLE VIDEO
60 REM                4 --- 1=640 X 200
70 REM                5 --- 0
80 REM                6 --- 0
90 REM                7 --- 0
100 OUT &H3D8,&H1A
110 REM then initialize 6845 crt controller data registers
120 FOR INDEX=0 TO &HF
125 OUT &H3D4,INDEX
130 READ BYTE
140 OUT &H3D5,BYTE
145 NEXT INDEX

147 STADR=0
150 REM if bit set in COLOUR then fill 6 scan line in appropriate bank
151 FOR COLOUR=0 TO 15

152 REM  test BLUE bit
155 IF COLOUR AND 1 THEN 156 ELSE 160
156 DEF SEG=&HB400:FOR ADDR=STADR TO STADR+239:POKE ADDR,&HFF:
    POKE ADDR+&H2000,&HFF:NEXT ADDR

157 REM test GREEN bit
160 IF COLOUR AND 2 THEN 161 ELSE 165
161 DEF SEG=&HB800:FOR ADDR=STADR TO STADR+239:POKE ADDR,&HFF:
    POKE ADDR+&H2000,&HFF:NEXT ADDR

164 REM test RED bit
165 IF COLOUR AND 4 THEN 166 ELSE 170
166 DEF SEG=&HBC00:FOR ADDR=STADR TO STADR+239:POKE ADDR,&HFF:
    POKE ADDR+&H2000,&HFF:NEXT ADDR

167 REM test INTENSITY bit
170 IF COLOUR AND 8 THEN 171 ELSE 175
171 DEF SEG=&HB000:FOR ADDR=STADR TO STADR+239:POKE ADDR,&HFF:
    POKE ADDR+&H2000,&HFF:NEXT ADDR

175 STADR=STADR+240
185 NEXT COLOUR
190 GOTO 190
195 REM these are the 6845 register values for this mode
200 DATA &H38,&H28,&H2D,&H0A,&H7F,&H06,&H64
210 DATA &H70,&H02,&H01,&H06,&H07,&H00,&H00,&H00,&H00

                 ****  END OF DOCUMENT ****