90



        N) = CHR$(BYTE): NEXT N
     35  DATA 104,162,16,76,86,228
     36  REM PLA,LDX,$10,JMP $E456
     40  OPEN #1,4,0,B$
     50  POKE 849,1: POKE 850,7: POKE 852,
        PEEK(88): POKE 853,PEEK(89): POKE
        856,70: POKE 857,30: POKE 858,4
     55  REM THESE POKES SET UP THE IOCB
     60  POKE 559,0: REM TURN OFF THE SCRE
        EN TO SPEED THINGS UP
     70  X = USR(ADR(ML$)): CLOSE #1
     80  POKE 559,Q: REM TURN IT BACK ON A
        GAIN

     Note that there is no provision to SAVE the color registers in this
     program, so I suggest you have them SAVEd after you have
     SAVEd the picture. It will make it easier to retrieve them if they are
     at the end of the file. You will have to make suitable adjustments
     when SAVEing a picture in other than GR.8 + 16 -- such as
     changing the total amount of screen memory to be SAVEd, POKEd
     into 856 and 857. Also, you will need a line such as 1000 GOTO
     1000 to keep a GTIA or + 16 mode screen intact. See the Atari
     column in InfoAge Magazine, July 1982, for more on this idea. See
     location 54277 ($D405) for some ideas on scrolling the screen
     RAM.

------------------------------------------------------------------------
A SHORT DIGRESSION
There are two techniques used in this hook for calling a machine
language program from BASIC with the USR command. One method
is to POKE the values into a specific address -- say, page six -- and
use the starting address for the USR call, such as X = USR(1536). For
an example of this technique, see location 632 ($278).

The other technique, used above, is to make a string (ML$) out of the
routine by assigning to the elements of the string the decimal
equivalents of the machine language code by using a FOR-NEXT and
READ-DATA loop. To call this routine, you would use X =
USR(ADR(ML$)). This tells the Atari to call the machine language
routine located at the address where ML$ is stored. This address will
change with program size and memory use. The string method won't
be overwritten by another routine or data since it floats around safely
in memory. The address of the string itself is stored by the string/array
table at location 140 ($8C).
------------------------------------------------------------------------

90             5A             OLDROW
     Previous graphics cursor row. Updated from location 84 ($54)