Engine RPM
Engine RPM is in increments of 40rpm. The maximum number in a 8-bit system is FFh or 255. Dividing engine RPM up into 40rpm increments allows a range of 0rpm to 10,200rpm.

Rev Limits ML1.1/ML1.2 & ML3.1 - For systems using a starter ring gear sensor.
Simply convert the number from hex to decimal and multiply by 40. 

Example: For a Rev Limit A3h
(A3h converts to 163)
Rev Limit = 40 * 163 = 6520rpm

Rev Limits ML4.1 & M2.1 - Systems with the 60/2 timing wheel.
The method of calculating rev limit has changed. It is now based on CPU clock speed. Two consecutive bytes are used to calculate rev limit.

Rev Limit Formula = 12,500,000 / ( RL1 X 2^RL2 )

Example:
RL1 = EDh  
RL2 = 03h
EDh converts to 237
Rev Limit = 12,500,000 / (237 X 2³) = 12,500,000 /  (237 X 8) = 6593rpm

Note: This formula may not apply to BMW and other system built after the late 80's.  Values other than 12,500,000 are used. I will update this page when I know more.