;create a node at address $0020, and another node at address $0040.
;The first node has a value of #$77, the second, #$99.
;create first node
LDA #$77
STA $20
LDA #$40
STA $21
LDA #$00
STA $22

;create second node
LDA #$99
STA $40
LDA #$FF  ;use $FFFF as the null pointer since the only thing that can be at address $FFFF is the high byte of the IRQ routine.
STA $41
STA $42