mov r1, #001        ; send 1
    call serial_send

; 9600 in PAL: (2.5us per cycle)
; 1 bit = 104.2 usec = 42 clocks
; 1.5 bits = 156.3 usec = 63 clocks
serial_send
    mov r1, #08h        ; eight bits
send_startbit
    orl P1,#00000001b   ; output 1
    mov r2,#a0      ; cycles to wait (x2)
wait_start
    djnz    r2,wait_start   ; decrement jump not zero
nextbit
    mov r2,#50      ; cycles to wait (x2)
    rrc a       ; rotate into carry
    jc  send_1      ; jump carry
send_0
    anl P1,#11111110b   ; output 0
    jmp wait96
send_1
    orl P1,#00000001b   ; output 1
    nop
wait96
    djnz    r2,wait96
    djnz    r0,nextbit
send_end
    anl P1,#11111110b
    ret