// Problem with assigning negative word constant (vwuz1=vbuc1)
.pc = $801 "Basic"
:BasicUpstart(main)
.pc = $80d "Program"
  .label screen = $400
main: {
    .label w = 2
    ldx #0
  __b1:
    txa
    and #1
    cmp #0
    beq __b3
    lda #<-1
    sta.z w
    lda #>-1
    sta.z w+1
    jmp __b2
  __b3:
    txa
    sta.z w
    lda #0
    sta.z w+1
  __b2:
    txa
    asl
    tay
    lda.z w
    sta screen,y
    lda.z w+1
    sta screen+1,y
    inx
    cpx #8
    bne __b1
    rts
}