Draws characters on a 13 by 20 grid. The program keeps the grid in memory from address 20000 up, fills it with inverse spaces and prints it, then asks for a row (1-13), a column (1-20) and a character code. It POKEs the code into the grid, clears the screen and reprints, so you build the picture one character at a time.
Written for the 4K ROM; the article notes that 8K users must change the POKE addresses to spare memory. Needs at least 4K RAM for the grid at 20000.
Published in Syntax June 1981 (Matrix Drawing).
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Source Code
1 LET A=19999
6 LET V=0
10 FOR I=1 TO 13
20 FOR J=1 TO 20
30 IF V>0 THEN GO TO 50
40 POKE A+(I*20)+J,128
50 PRINT CHR$(PEEK(A+(I*20)+J));
60 IF J=20 THEN PRINT " "
70 NEXT J
80 NEXT I
90 INPUT D
100 INPUT B
110 INPUT C
120 POKE A+(D*20)+B,C
130 CLS
131 CLEAR
135 LET V=1
137 LET A=19999
140 GO TO 10Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.