Decoded: Rogue (1980) by Toy, Arnold, Wichman
DOS version (1983) by Mel Sibony and Jon Lane
Source file: CURSES.C
Beginner friendly, line-by-line code walkthrough by MaiZure

CURSES.C provides console management routines for I/O control. This seems like
a custom implementation ported to DOS specifically for Rogue

Original code:
https://britzl.github.io/roguearchive/

Original code with line numbers
http://www.maizure.org/projects/decoded-rogue/CURSES_linenum.txt



1     COMMENT
2     COMMENT
3     COMMENT
4     Includes the game header
5     Includes the curses header
6     BLANK
7     Imports the memory allocation call linked from SBRK.ASM
8     COMMENT
9     COMMENT
10    COMMENT
11    Initialize screen dimension globals for text mode - 25x80
12    Declare flag signalling if screen state has been saved for later
13    Declare a flag for the cursor state - on or off
14    Declare an integer to hold the character display mode (fore/back color)
15    Declare a global holding the previously posted memory page
16    Declare a flag enabled if we're checking monitor retrace state
17    BLANK
18    Initializes the screen data segment, 0xB800 is the base memory page for
      CGA/EGA/VGA. Note that the original Monochrome starts at 0xB000
19    Declare an integer to hold the window data segment
20    BLANK
21    Declare a pointer to the saved screen to dump to or restore from
22    Declare the screen mode
23    Declare the tab size
24    Declare the current memory page number
25    BLANK
26    Define a macro for the maximum number of character format attributes
27    Initialize an array of character attributes for color monitors
28    A color attribute (this ordering is mostly unique -- never standardized)
29    A color attribute
30    A color attribute
31    A color attribute
32    A color attribute
33    A color attribute
34    A color attribute
35    A color attribute
36    A color attribute
37    A color attribute
38    A color attribute
39    A color attribute
40    A color attribute
41    A color attribute
42    A color attribute
43    A color attribute
44    A color attribute
45    Blank (also black)
46    End of color monitor attributes
47    BLANK
48    Initialize attribute array for monochrome monitors
49    A monochrome attribute
50    The same monochrome attribute
51    Look Monochrome only has 1 color right?
52    But we still need compatability with the color code right?
53    Guess we have to plug this array with the exact same attribute
54    Over
55    and Over
56    and Over
57    and Over
58    ...
59    Yup, still just the same color
60    zzzzz
61    Oh look, a different attribute!
62    And we're back to the same old attribute
63    A third attribute!
64    Old faithful again
65    The same third attribute.
66    Black -- and end of out monochrome attributes
67    End of monochrome attribute data
68    BLANK
69    Declare a generic pointer to one of the attribute tables
70    BLANK
71    Declare globals to cache the cursor position...avoids interrupts
72    Declare a global array for a screen row of data
73    BLANK
74    Declares an array of characters used for drawing double border boxes
75    A set of ASCII characters from code page 437
76    End of character array
77    BLANK
78    Declares an array of characters used for drawing single border boxes
79    A set of ASCII characters from code page 437
80    End of character array
81    BLANK
82    Declares an array of characters used for drawing thick border boxes
83    A set of ASCII characters from code page 437
84    End of character array
85    BLANK
86    Declares an array of characters used for blank boxes...black border?
87    A set of ASCII characters from code page 437
88    End of character array
89    BLANK
90    COMMENT
91    COMMENT
92    COMMENT

CLEAR THE SCREEN

93    Defines clear with no argument
94    BLOCK START - clear, clears the screen
95    If we're currently processing the saved screen state buffer...
96    Copy the saved screen data to the buffer
97    Otherwise this is a basic clear screen
98    Set entire screen memory page to 0
99    BLOCK END - 
100   BLANK
101   BLANK
102   COMMENT
103   COMMENT
104   COMMENT

ENABLE/DISABLE BLINKING CURSOR

105   Define cursor with one argument
106   Argument 1 is the flag for the desired state (on or off)
107   BLOCK START - cursor, turns cursor on and off
108   Declare a variable for the old cursor state
109   Declare an unused variable (dead code)
110   BLANK
111   BLANK
112   If we're attempting to turn on a cursor that's already on...
113   Just return, don't bother wasting interrupt time
114   Set the old state to the current state
115   Update the current state to the requested state
116   BLANK
117   Set the AH = 0x01 (changing cursor state)
118   If we're turning on the cursor...
119   BLOCK START - Turn on cursor
120   In color mode, set cursor to CX=0x0607 (blinking at ~half size)
121   Invoke the actual interrupt - BIOS 0x10
122   Move the cursor to the most recent position
123   BLOCK END - Turn on cursor
124   Otherwise we're turning off the cursor
125   BLOCK START - Turn off cursor
126   Set CX = 0xf00 (invisible on EGA/VGA)
127   Invoke BIOS interrupt 0x10 with new AX/CX values
128   BLOCK END - Turn off cursor
129   Return the previous state of the cursor (easy to save and restore state)
130   BLOCK END - cursor
131   BLANK
132   BLANK
133   COMMENT
134   COMMENT
135   COMMENT

GET CURSOR POSITION FROM CACHE

136   Define getrc with two arguments
137   Arguments are pointers to the the cached row and column values
138   BLOCK START - getrc, updates the cursor position pointers to the cache
139   Set the row pointer to our global cursor row cache variable
140   Set the column pointer to our global cursor column cache variable
141   BLOCK END - getrc
142   BLANK

GET CURSOR POSITION FROM BIOS

143   Defines real_rc with three arguments
144   Argument 1 is memory page number, 2 and 3 are pointers to position vars
145   BLOCK START - real_rc
146   COMMENT
147   COMMENT
148   COMMENT
149   Prepare to read cursor position (AH = 0x03)
150   Put the memory page number in to BH by byte shifting in to BX
151   BLANK
152   Invoke the BIOS interrupt (0x10) - Position in DX, size in CX (ignored)
153   BLANK
154   Point the row to the value in DH (have to right shift a byte)
155   Point the column to the value in DL (mask only the lower byte)
156   BLOCK END - real_rc
157   BLANK
158   COMMENT
159   COMMENT
160   COMMENT

CLEAR A SCREEN ROW

161   Declare clrtoeol with no arguments
162   BLOCK START - clrtoeol, clear a row on the screen
163   Declare row and column variables
164   BLANK
165   If we're not even looking at the current screen...
166   Don't bother
167   Otherwise, get the current cursor position
168   Clear the whole row
169   BLOCK END - cleartoeol
170   BLANK

MOVE CURSOR TO POSITION AND PRINT A STRING

171   Declare mvaddstr with three arguments
172   Arguments 1 and 2 are row and column positions
173   Argument 3 is a pointer to the string
174   BLOCK START - mvaddstr, prints a string starting at a position
175   Move the cursor to the position
176   Print the string
177   BLOCK END - mvaddstr
178   BLANK

MOVE CURSOR TO POSITION AND PRINT A CHARACTER

179   Defines mvaddch with three arguments
180   Arguments 1 and 2 are row and column positions
181   Argument 3 is the character to print
182   BLOCK START - mvaddch, prints a character at a position
183   Move cursor to position
184   Print the character
185   BLOCK END - mvaddch
186   BLANK

MOVE CURSOR TO POSITION AND READ THE CURRENT CHARACTER

187   Defines mvinch with 2 arguments
188   Arguments 1 and 2 are the cursor position to read
189   BLOCK START - mvinch, Returns a character at a position
190   Move cursor to position
191   Return the first byte at that position (ASCII code)
192   BLOCK END - mvinch
193   BLANK
194   COMMENT
195   COMMENT
196   COMMENT
197   COMMENT
198   BLANK

PRINT A CHARACTER TO CURRENT POSITION (GAME-BASED, NOT GENERAL PURPOSE)

199   Declares addch with one argument
200   Argument 1 is the character to print
201   BLOCK START - addch, prints a character to the current position
202   Declare row and column position integers
203   Declare upated row and column integers
204   Declare a character to hold the old attribute
205   BLANK
206   Set the old attribute to the current global attribute setting
207   BLANK
208   If we're using a color screen...
209   BLOCK START - color printing, we have to update attr with pretty stuff
210   COMMENT
211   If we're printing the regular base color used in rooms...
212   SWITCH on the room object to print
213   BLOCK START - Switch on character to update color
214   CASE character is a door
215   CASE character is a vertical wall
216   CASE character is a horizontal wall
217   CASE character is an upper-left corner
218   CASE character is an upper-right corner
219   CASE character is a lower-left corner
220   CASE character is a lower-right corner
221   Change the current color to brown
222   Break out of color changes
223   CASE character is the floor
224   Change the current color to light green
225   Break out of color changes
226   CASE character is the stairs
227   Change the current color to black text, green background
228   Break out of color changes
229   CASE character is a visible trap
230   Change the current color to magenta
231   Break out of color changes
232   CASE character is gold
233   CASE character is the player avatar
234   Change the current color to yellow
235   Break out of color changes
236   CASE character is a potion
237   CASE character is a scroll
238   CASE character is a wand/staff
239   CASE character is armor
240   CASE character is an amulet
241   CASE character is a ring
242   CASE character is a weapon
243   Change the current color to light blue
244   Break out of color changes
245   CASE character is food
246   Change the current color to red
247   Break out of color changes
248   BLOCK START - Switch on character to update color
249   COMMENT
250   Otherwise, check if the color is the default passage color
251   SWITCH on the passage object to rpint
252   BLOCK START - Switch on character to update color
253   CASE character is food
254   Change the current color to red background, black text
255   Break out of color changes
256   CASE character is gold
257   CASE character is the player
258   Change the current color to yellow text, white background
259   Break out of color changes
260   CASE character is a potion
261   CASE character is a scroll
262   CASE character is a wand/staff
263   CASE character is armor
264   CASE character is an amulet
265   CASE character is a ring
266   CASE character is a weapon
267   Change the current color to blue background, black text
268   Break out of color changes
269   BLOCK END - Switch on character to update color
270   For all other color cases...
271   Stairs are black text on green background
272   End check for color screens, the rest is color and mono handling
273   BLANK
274   Get the current row and column
275   If the current character is a newline...
276   And if we're at the end of a page...
277   Scroll the screen up one line
278   Move the cursor to the last screen line
279   Otherwise, we're in the middle of the screen somewhere so...
280   Move the cursor down one line
281   Set the cursor attribute to the old attribute
282   Return the current column
283   End check for newline character
284   Print the character that is properly position with the correct color
285   Move the cursor to the right
286   Save the color attribute we just used
287   COMMENT
288   COMMENT
289   COMMENT
290   Return current row
291   BLOCK END - addch
292   BLANK

PRINT A STRING TO THE SCREEN

293   Defines addstr with one argument
294   Argument 1 is a pointer to the string
295   BLOCK START - addstr, prints a string to the screen
296   While there is a valid character...
297   Print character to the screen and increment pointer to next character
298   BLOCK END - addstr
299   BLANK

CHANGE COLOR

300   Define set_attr with one argument
301   Argument 1 is the input attribute index or a raw attribute
302   BLOCK START - set_attr
303   If the input attribute is a valid index...
304   Set the current attribute from the table
305   Otherwise...
306   Assume that the input is the attribute, not an index
307   BLOCK END - set_attr
308   BLANK

GENERATE ERROR (NOT USED)

309   Defines error with seven arguments
310   Argument 1 is the error row on the screen
311   Argument 2 is the error message
312   Arguments 3 to 7 are the message arguments
313   BLOCK START - error, prints an error (not used)
314   Declares local row and columns
315   BLANK
316   Get the current row and column
317   Move the cursor to the beginning of the error line
318   Clear the line
319   Print the error message
320   Return the cursor to the current position
321   BLOCK END - error
322   BLANK
323   COMMENT
324   COMMENT
325   COMMENT
326   COMMENT
327   BLANK

SET CURSOR (DEAD CODE)

328   Defines set_cursor with no arguments
329   BLOCK START - set_cursor, dead code
330   COMMENT
331   COMMENT
332   COMMENT
333   COMMENT
334   COMMENT
335   BLOCK END - set_cursor
336   BLANK
337   COMMENT
338   COMMENT
339   COMMENT
340   COMMENT
341   COMMENT
342   COMMENT

INITIALIZE GAME WINDOW

343   Defines winit with one argument
344   Argument 1 is unused, but was probably the default drive letter
345   BLOCK START - winit, initializes the game window
346   Declare an iterator and a counter
347   Import the current datasegment
348   BLANK
349   COMMENT
350   COMMENT
351   COMMENT
352   Set AH to 0xF to get the current video mode and active memory page
353   Invoke the interrupt
354   Save the memory page number from the result in BX
355   Get the screen type
356   COMMENT
357   COMMENT
358   COMMENT
359   COMMENT
360   COMMENT
361   Set the number of rows on the screen to 25
362   Set the number of columns on the screen to 80
363   Set the video memory base to 0xB800
364   Set the current color mode to monochrome
365   BLANK
366   BLOCK START - SWITCH on the screen type
367   COMMENT
368   COMMENT
369   COMMENT
370   CASE type 1 (color, 40x25 text)
371   Set attribute table to color
372   CASE type 0 (monochrome, 40x25 text)
373   Set columns to 40
374   Break from check for video type
375   BLANK
376   COMMENT
377   COMMENT
378   COMMENT
379   CASE type 3 (color, 80x25 text)
380   Set the attribute table to color
381   CASE type 2 (monochrome, 80x25 text)
382   Break - this is the default init from above
383   CASE type 7 (monochrome, 80x25)
384   This is a true Monochrome (tm) device - memory base is at 0xB000
385   Disable retrace check
386   Break from check for video type
387   COMMENT
388   COMMENT
389   COMMENT
390   COMMENT
391   COMMENT
392   COMMENT
393   COMMENT
394   COMMENT
395   COMMENT
396   CASE any other screen mode..
397   Move the cursor to the bottom left
398   Print an error message and fail out of program
399   End select for video mode
400   COMMENT
401   COMMENT
402   COMMENT
403   Get the current cursor position
404   Initialize backup video buffer with 4kb but if it fails...
405   The window segment is invalid
406   Point the backup buffer to the known good flags segment
407   But if we're using a monochrome monitor...
408   Fail out due to lack of memory
409   Otherwise, memory allocation was successful so..
410   Nibble align the value...why?
411   Grab buffer segment base address by offsetting 12 bits in to the dataseg
412   End memory allocation for window save buffer
413   Loop through each row
414   Count the byte offset for each row and save
415   Allocate (and leak..?) 2 bytes. Possibly for alignment guarantee
416   Change to the 4th memory page
417   If we weren't already on the 4th page...
418   Clear the screen (memory)
419   Move the cursor to the current position
420   If this is a PC Jr..
421   Disable retrace check
422   BLOCK END - winit
423   BLANK

FORCE COLOR TO BLACK & WHITE

424 
425   BLOCK START - forcebw, sets mode to black and white
426   Points the attribute table to the monochrome table
427   BLOCK END - forcebw
428   BLANK
429   COMMENT
430   COMMENT
431   COMMENT
432   COMMENT
433   COMMENT

SAVE THE CURRENT SCREEN STATE

434   Define wdump with no arguments
435   BLOCK START - wdump, outputs the screen state to backup buffer
436   If memory allocation failed, push level flags out to the screen
437   In any case, read the screen buffer and save it to savewin
438   Screen is now saved
439   BLOCK END - wdump
440   BLANK

SAVE THE CURRENT SCREEN FLAGS

441   Defines sav_win with no arguments
442   BLOCK START - sav_win, saves the level flags to video memory
443   Check if we're on Plan B of backup buffer
444   Send the current level flags out to video memory base page
445   Return pointer used
446   BLOCK END - sav_win
447   BLANK

RESTORE THE LEVEL FLAGS

448   Defines res_win with no arguments
449   BLOCK START - res_win, restores the level flags stored in video memory
450   Checks if backup memory allocation originally failed...
451   If so, we need to bring the flags back via DMA
452   BLOCK END - res_win
453   BLANK
454   COMMENT
455   COMMENT
456   COMMENT
457   COMMENT

RESTORE THE SAVED SCREEN STATE

458   Defines wrestor with no arguments
459   BLOCK START - wrestor, loads a save console screen from memory
460   Send stored screen data back to video memory
461   Get flags back stored in page 0 of video memory
462   Screen is no longer saved
463   BLOCK END - wrestor
464   BLANK
465   COMMENT
466   COMMENT
467   COMMENT
468   COMMENT

SHUT DOWN THE SCREEN

469   Defines wclose with no arguments
470   BLOCK START - wclose, closes the output window
471   BLANK
472   COMMENT
473   COMMENT
474   COMMENT
475   If we have a valid video mode...
476   Turn the cursor on
477   If we've changed pages for some reason
478   Move back to the desired page
479   BLOCK END - wclose
480   BLANK
481   COMMENT
482   COMMENT
483   COMMENT
484   BLANK

DRAW A GENERAL PURPOSE BOX

485   Define box with four arguments, the 4 corner positions of the box
486   BLOCK START - box, draws a box on the screen using input coordinates
487   Draw a styled box with double borders at the given position
488   BLOCK END - box
489   BLANK
490   COMMENT
491   COMMENT
492   COMMENT
493   COMMENT
494   BLANK

DRAW A STYLIZED BOX

495   Declares vbox with five arguments
496   Argument 1 is the character set structure to draw the box with
497   Arguments 2-5 are the 4 corners of the box
498   BLOCK START - vbox, draws an ASCII box on the screen 
499   Declare an iterator and a state flag
500   Declare two integers for row and column position
501   BLANK
502   Turn off the cursor and save its previous state
503   Get the starting cursor position
504   BLANK
505   COMMENT
506   COMMENT
507   COMMENT
508   Move the cursor to the upper left of the box (+1 to draw corners last)
509   Draw the top box horizonal
510   Move cursor to bottom left +1
511   Draw the bottom box horizonal
512   COMMENT
513   COMMENT
514   COMMENT
515   Loop from the top of the box to the bottom
516   Draw the left verical wall
517   Draw the right vertical wall
518   Repeat loop
519   COMMENT
520   COMMENT
521   COMMENT
522   Draw upper left corner
523   Draw upper right corner
524   Draw lower left corner
525   Draw lower right corner
526   BLANK
527   Move the cursor to the original position
528   Restore the cursor to its previous state
529   BLOCK END - vbox
530   BLANK
531   COMMENT
532   COMMENT
533   COMMENT

CENTER TEXT ON THE SCREEN

534   Define center with two arguments
535   Argument 1 is the row to draw the string
536   Argument 2 is the string to draw
537   BLOCK START - center, centers a string on the screen
538   Draw the string starting at colums, minus string length divided by 2
539   BLOCK END - center
540   BLANK
541   BLANK
542   COMMENT
543   COMMENT
544   COMMENT

PRINT FORMATTED MESSAGE

545   Define printw with nine arguments
546   Argument 1 is a message to output
547   Arguments 2-9 are formatted argumented
548   BLOCK START - printw, prints an (almost) variadic string to the screen
549   Declare a temporary buffer of 132 bytes
550   Output the formatting string to the global print buffer
551   Print the print buffer
552   BLOCK END - printw
553   BLANK

SCROLL ROW UP

554   Declare scroll_up with three arguments
555   Arguments are the start/end pointers on the row and the number of lines
556   BLOCK START - scroll_up, scrolls a screen region up 1 line
557   Set up for BIOS INT 0x10 call by putting AH=0x6, AL = scroll distance
558   Set up BX for the attributes of new blank lines
559   Left bound to CX
560   Right bound to DX
561   Invoke software interrupt
562   Move the cursor to the end of the changed row
563   BLOCK END - scroll_up

SCROLL ROW DOWN

564   Declare scroll down with three arguments
565   Arguments are the start/end pointers on the row and the number of lines
566   BLOCK START - scroll_dn, scrolls a screen region down 1 line
567   Set up for BIOS INT 0x10 call by putting AH=0x7, AL = scroll distance
568   Set up BX for the attributes of new blank lines
569   Left row position in CX
570   Right row position in DX
571   Invoke INT 0x10
572   Move the cursor to the start of the changed row
573   BLOCK END - scroll_dn
574   BLANK

SCROLL WHOLE SCREEN UP 

575   Define scroll with no arguments
576   BLOCK START - scroll, scrolls the screen up one line
577   Scroll the entire screen up 1 line
578   BLOCK END - scroll
579   BLANK
580   BLANK
581   BLANK
582   COMMENT
583   COMMENT
584   COMMENT
585   COMMENT
586   COMMENT

CLEAR A REGION OF THE SCREEN

587   Define blot_out with four arguments (the four corners)
588   BLOCK START - blot_out, clear a screen region
589   Set up AX like a scroll up until it's off the screen
590   New rows have attribute 0x07
591   Set up left side of the row change
592   Set up right side
593   Invoke interrupt 0x10
594   Move the cursor to the upper left position of the cleared box
595   BLOCK END - blot_out
596   BLANK

REPEATEDLY PRINT A CHARACTER

597   Define repchr with two arguments
598   Argument 1 is the character two print. Arg 2 is the number of repeats
599   BLOCK START - repchr, repeats a character
600   While there is still work to do...
601   Print character
602   Advance cursor column 1 space
603   End print loop
604   BLOCK END - repchr
605   BLANK
606   COMMENT
607   COMMENT
608   COMMENT

PATCH SCREEN AFTER CTRL-BREAK

609   Define fixup with no arguments
610   BLOCK START - fixup, clear a screen column
611   Clear the region around the cursor
612   BLOCK END - fixup
613   BLANK
614   COMMENT
615   COMMENT
616   COMMENT
617   BLANK

ANIMATED CLEAR SCREEN

618   Define implode with no arguments
619   BLOCK START - implode, clear screen animation
620   Define a lot of helpers, including a column incrementor
621   BLANK
622   Set an invariant to be 21 or 22, depending on screen size
623   COMMENT
624   COMMENT
625   COMMENT
626   If there is nothing on the screen...
627   Don't bother - clear memory
628   Exit function
629   End check for empty screen
630   Set a delay factor for visible drawing. Monochrome is FAST so big delay
631   Loop across various positions through the screen in patchwork fashion
632   Draw single boxes of shrinking sizes
633   Start a delay loop
634   Repeat delay loop
635   Loop across the current row
636   Draw spaces from the left
637   Draw spaces from the right
638   End row loop
639   Draw another box
640   Repeat this mess until the screen has finished drawing
641   BLOCK END - implode
642   BLANK
643   COMMENT
644   COMMENT
645   COMMENT
646   COMMENT

SCREEN SCROLL OUT ANIMATION

647   drop_curtain returns address of the old data segment
648   Define drop_curtain with no arguments
649   BLOCK START - drop_curtain, slide out screen updating animation
650   Declare local integers for row/column position, an interator and delay
651   BLANK
652   If we're not looking at an active screen...
653   Then nothing to fade out - return
654   Store the screen segment
655   Save the screen data in to the backup buffer
656   Turn off the cursor
657   Set a delay - high if monocrhome since it's fast
658   Set the foreground color to green
659   Draw a single-border box around the whole screen
660   Set color to yellow
661   Loop through all rows
662   Move the cursor to the start of the row
663   Print the code page 437 character for dotted-box across the row
664   Delay for the desired cycles
665   Repeat delay
666   End drawing across rows
667   Reset the screen data segment to the saved screen
668   Move the cursor to the start
669   Undo character highlighting
670   BLOCK END - drop_curtain
671   BLANK

SCREEN SCROLL IN ANIMATION

672   Define raise_curtain with no arguments
673   BLOCK START - raise_curtain, slide in screen updating effect
674   Declare iterators, a position variable, and a delay
675   BLANK
676   If we're looking at the saved screen buffer (nothing on screen)
677   Then there's nothing to do - return
678   Restore the old data segment
679   Set a delay so we can see animations
680   Loop through each row
681   Output the saved window segment back to the screen
682   Delay on each row
683   Repeat delay
684   End loop through each row
685   BLOCK END - raise_curtain
686   BLANK

SWAP VIDEO MEMORY PAGES

687   Define switch_page with one argument - the memory page number
688   BLOCK START - switch_page, swaps video memory page
689   Ddeclare an integer for the page size
690   BLANK
691   If the screen is monochrome
692   Start on page 0
693   Return
694   End check for monochrome
695   If the screen is small, only 40 characters wide
696   Then use page sizes of 2kb
697   Otherwise...
698   Page size is 4kb
699   Set AH to 0x05 - setting active page in video memory
700   Invoke the interrupt
701   Set the screen data segment is at base 0xB800 plus the page offset
702   Set the page number global to the input page number
703   BLOCK END - switch_page
704   BLANK

GET VIDEO MODE FROM BIOS

705   Defines get_mode with one unused argument
706   BLOCK START - get_mode, returns the video mode using BIOS
707   Bring in register structure
708   BLANK
709   Assign AH to 0x0F
710   Invoke BIOS Interrupt 0x10 to get the current video mode
711   Return video mode to caller
712   BLOCK END - get_mode
713   BLANK

GENERIC BIOS CALL
Apparently used for video...but you can insert ANY INT 10 call in here...hmm

714   Define video mode with argument 1 as the desired video mode
715   BLOCK START - video_mode, sets the video mode
716   Bring in the register structure
717   BLANK
718   Assign AX to the video mode
719   Invoke BIOS Interrupt 0x10 to change video modes
720   Return the resulting video mode flag
721   BLOCK END - video_mode
722   EOF˙