Abstract: A microcomputer-based electronic control system for a full time four wheel drive torque transfer case monitors the relative slip between the front and rear output shafts of the transfer case, and generates a signal to engage an electromagnetic clutch for a predetermined time period in the event a predetermined slip threshold is exceeded. The control system continuously interrogates two Hall effect sensors positioned over toothed wheels on the front and rear outputs of the transfer case. Tooth counts are stored in two numerical stacks (one for each sensor), the depth of which may be adapted to the requirements of the particular design. Upon detecting a tooth count, the system adds the count to the sensor's current stack register and pushes all of the registers of the other stack down one register. The last register is pushed out or deleted from the stack memory.