Miata Turbo Forum - Boost cars, acquire cats.

That map is straight from the ROM and is just one of the factors used to calculate the fuel sum. It's several years since I looked at it so I've forgotten most of it, but I pulled this quote from my notes of the time (the reading from that map is stored in location 00F8):

Code:

0102:  Main Fuelling sum  is calculated in a subroutine at A0B2



Start with a value of $0040, then add 8 bit values from 00F5, 00F8 and 00F7 and multiply the result by 4.



Add 8 bit value from 00FB and multiply the result by 8.



Add 16-bit values from 00FC, 00F9 and 0104, multiply result by the (8-bit) value in 0106, producing a 3 byte result.



Multiply that result by 2 then take only the top 2 bytes of the answer.



Store the result in 0102 (limited to $499A maximum).



So the sum is;   

        0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

        0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0

        0 0 0 [ . . 00F5 . . ]0 0 0 0 0

        0 0 0 [ . . 00F8 . . ]0 0 0 0 0

        0 0 0 [ . . 00F7 . . ]0 0 0 0 0

        0 0 0 0 0[ . . 00FB . . ] 0 0 0

        [. . . . . . . 00FC . . . . . ]

        [. . . . . . . 00F9 . . . . . ]

  +     [. . . . . . . 0104 . . . . . ]

                                               





((((($0040 + 00F5 + 00F8 + 00F7) x 4) + 00FB) x 8) + 00FC + 00F9 + 0104) x 0106 x 2 /256







00F5         This might be acceleration enrichment.

00F8         This is the reading from the AFR/fuel map

00F7         might be cold start enrichment

00FB        Just might be lambda correction

00FC        dunno

00F9        dunno

0104        always zero



0106        the multiplier. Seems to be $80 (x 2/256 = unity) or $00 (which would be a fuel cut)