Hardware Architecture

The design of the Powertrain Control Module (PCM) can be broken up into about eight major sections. The main micro controller, a Motorola MC68HC16Z2, is attached to a 256k byte memory device (flash memory) which is programmed after manufacture of the module. (This memory can be reprogrammed at the factory or at a dealership. The MC68HC11 D3 and MC68HC11 K4 microcomputers have memories which are permanently programmed during their manufacture, and therefore cannot be reprogrammed.) The microcomputers communicate over a bus which allows for rapid transmission of high priority messages. The Z2 executes the primary powertrain control strategy; transmits fuel and spark requirements to the D3 and K4; communicates with outside devices; and processes 14 analog inputs and about half of the one bit inputs and outputs. The D3 microcomputer controls fuel injector timing pulses and a small number of one bit inputs and outputs. The K4 controls spark timing pulses, processes 8 analog inputs and a number of one bit inputs and outputs.

Other major sections of the PCM design include the power supply, input conditioning circuits, output driver circuits, serial communication interface circuits, and a device which controls ignition coil currents.