Atari 400 Technical Reference Manual page 384

ERR LINE ADDR 81 82 83 84 DISPLAY HANDLER -- 10-30-78 DISPLC PAGE 123
5545 FE31 A5 7E LDA COUNTR
5546 FE33 E9 01 S8C #1
5547 FE35 85 7E STA
COUNTR
5548 FE37
AS 7F LDA
COUNTR+1
5549
FE39 E9 00 S8C
#0
5550 FE3B 85 7F STA COUNTR+1
5551 FE3D 30 03 8MI DRAW10
5552 FE3F 4C 90 FD JMP DRAW4A
5553 FE42 4C 34 F6 DRAWI0: JMP RETURl