Calling Routine For Marquee

Kenneth Finn
Bedford, NY

Building on an intriguing video display technique ("Marquee," February 1982, p. 135), this program makes it easy to add horizontal scrolling which is independent of BASIC. Line 20 can accept a string either from the keyboard or a DATA statement READ. The rest is automatic and, because this routine uses interrupts, it is "transparent" to other things BASIC is doing at the time. It works as printed for Upgrade and 4.0 BASIC PET/CBM's. If you have an 80-column screen, change the 40 in line 864 to an 80. Change the speed by changing the five in line 864.

"Marquee." by Mark Bernstein (COMPUTE!, February 1982, #21), is an exciting program that gives the capability to make the top line of the screen into a billboard with strings moving from right to left across it.

Since the program is in machine language, it requires a special set-up to use from BASIC. The way the program was originally written, you load the Accumulator and X register of the 6502 with the address of the string you want printed before calling the routine. In his article he coded such a string for demonstration. However, when you are writing a BASIC program, setting up such a string is not so easy.

The following routine can be used in any BASIC program to make Marquee work simply and easily for you. The trick is that locations 68 and 69 contain an address for the location of the last referenced string in the BASIC program. Thus, we must make our BASIC program reference the correct string, then tack on a chr$(0) to it as an end marker, and then indirectly get its address. The following program does this for you in the form of a subroutine.

 10 INPUT /ENTER STRING/;A$
 20 LET A$ = A$ + CHR$(0) : GOSUB100
 30 REM
 40 GOTO 10
 50 END
 60 REM
 70 REM
100 REM MARQUE CALLING SUBROUTINE
103 REM
105 IF PEEK (145) <> 46 THEN 105
110 POKE1009,PEEK((PEEK (68) + 2 + PEEK (69) *256): REM HI BYTE
120 POKE 1011,PEEK((PEEK(68) + 1 + PEEK(69)*256): REM LO BYTE
130 SYS1008:RETURN
140 REM
150 REM

The above routine makes using Marquee from BASIC simple and makes the routine even more valuable.

10 GOSUB800
20 INPUT A$ : A$ = A$ + CHR$ (0) : REM OR READ A$ (FROM A DATA STATEMENT IN PROGRAM)
30 POKE1009, PEEK (PEEK (68) + PEEK (69) * 256 + 2) : REM HIGH BYTE
40 POKE1011, PEEK (PEEK (68) + PEEK (69) * 256 + 1) : REM LOW BYTE
50 SYS1008
60 END
800 REM MARQUEE MACHINE LANGUAGE
810 FOR ADRES = 864 TO 1015 : READ DATTA : POKE ADRES, DATTA : NEXT ADRES
820 RETURN
864 DATA 40, 0, 5,85, 228, 7
870 DATA 5, 40, 160, 1, 185, 0
876 DATA 128, 153, 255, 127, 200, 204
882 DATA 96, 3, 208, 97, 3, 240, 15
894 DATA 192, 255, 240, 11, 200, 140
900 DATA 101, 3, 172, 96, 3, 153
906 DATA 255, 127, 96, 172, 96, 3
912 DATA 169, 32, 153, 255, 127, 238
918 DATA 103, 3, 173, 103, 3, 205
924 DATA 96, 3, 176, 48, 96, 172
930 DATA 101, 3, 177, 0, 41, 191
936 DATA 96, 141, 0, 0, 142, 1
942 DATA 0, 169, 0, 141, 103, 3
948 DATA 141, 101, 3, 173, 144, 0
954 DATA 141, 99, 3, 173, 145, 0
960 DATA 141, 100, 3, 120, 169, 223
966 DATA 141, 144, 0, 169, 3, 141
972 DATA 145, 0, 88, 96, 120, 173
978 DATA 99, 3, 141, 144, 0, 173
984 DATA 100, 3, 141, 145, 0, 88
990 DATA 96, 206, 102, 3, 16, 9
996 DATA 32, 104, 3, 173, 98, 3
1002 DATA 141, 102, 3, 108, 99, 3
1008 DATA 162, 3, 169, 248, 32, 169
1014 DATA 3, 96