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%META:TOPICINFO{author="mind-eracer" date="1122408060" format="1.0" version="1.1"}%
This formula is used to convert values in the high cam table scales to real-world RPMs. If ''x'' is an 8-bit high-cam scale RPM value,
- Hi Cam RPM?(''x'') = 1875000*''x'' / 53248
53248=D000h. Here is how it's calculated using standard integer fixed-point math tricks:
| |MOV er2, 0ach|; 0805 0 02 00 B5AC4A
| |MOV er0, #0d000h|; 0808 0 02 00 449800D0
| |CLR A|; 080C 1 02 00 F9
| |DIV|; 080D 1 02 00 9037
| | |; DIV = (er0, A) <-- (er0, A) / er2; in this case, 0xd0000000 / (1875000/RPM)
| | |; using bytes instead of words, (r1,r0,Ah,Al) <-- (r1,r0,Ah,Al) / (r5,r4)
|||''... store the high bit of A, decide whether the divide overflowed, etc...''
| |LB A, r0|; 0817 0 02 00 78
| | |;r0 is the least significant byte of er0, which is the most significant word of the quotient!
| |JNE label_081f|; 0818 0 02 00 CE05
|||''... overflow conditions, etc...''
|label_081f:|STB A, 0aah|; 081F 0 02 00 D5AA |
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