Matrix Drawing

This 4K ROM program draws characters on a 13 by 20 matrix. To operate, type RUN. When the computer expects input, enter a number (1-13), indicating which line you want a character on. The second input (1-20), designates the column. The third input is the character code of the character you want at the designated location. For 8K, change all POKEs to write to spare memory.

   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 10
Syntactic Sum=18662,4K