Here is the relevant code:
A0CF ldaa L8057 ;IP PULSE DIVISOR
A0D2 staa *L00C0
A0D4 jsr LF0EB
'this much is obvious so far...then:
-------------------------------------------------------------------------
F0EB LF0EB:ldx #0x4002
F0EE bclr 0x00,x,#0x80
F0F1 ldaa *L00C0
F0F3 jsr LFD85
F0F6 bset 0x00,x,#0x80
F0F9 ldx #0x86C0
F0FC brclr 0x00,x,#0x80,LF108
F100 anda #0x7F
F102 brclr *L0030,#0x04,LF108
F106 oraa #0x80
F108 LF108:staa *L00BF
F10A rts
------------------------------------------------------------
;-------------------------------------------------------
; THINK THIS IS TRANSMIT ROUTINE - COMMANDS ARE DIFFERENT THAN $8D,
; BUT ROUTINE USED IN SIMILAR WAY
; XMIT ON SERIAL SHIFT REG, (SSR)
;---------------------------------------------------------
FD85 LFD85:pshx
FD86 staa L4000
FD89 ldx #0x4001
FD8C bclr 0x00,x,#0x80
FD8F ldaa #0x16
FD91 clc
FD92 LFD92:brset 0x00,x,#0x80,LFD9C
FD96 deca
FD97 bne LFD92
FD99 sec
FD9A bra LFD9F
FD9C LFD9C:ldaa L4000
FD9F LFD9F:pulx
FDA0 rts
Now for some background. This is the code that controls the pulses sent to my car's speedometer. Originally it had a transmission that sent a roughly 24000 pulses per mile signal and there was a value here that converted it to a roughly 4000 ppm signal. The location at L8057 gets a byte that sort of acts as a divisor. "Sort of" is the key phrase. My new transmission sends a roughly 60,000ppm signal. I would like to understand the logic of these routines so that I can burn in the correct value to run my speedometer again.
