3500 4x2 Pickup V10-488 8.0L Magnum (1996)
Powertrain Control Module: Description and Operation
Architecture
Hardware
HARDWARE ARCHITECTURE
The design of the Powertrain Control Module (PCM) can be broken up into about eight major sections. The main microcontroller, 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 MC68HC11D3 and MC68HC11K4 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.
Software
SOFTWARE ARCHITECTURE
The 68HC16Z2 microcontroller is the main computing unit of the Powertrain Control Module (PCM). The 68HC11D3 and K4 microcontrollers
control fuel and spark respectively. They handle the critical timing requirements of their tasks, communicating with the Z2 using high level
commands.
The Z2 operating system is the heart of the software and was written expressly for this PCM. Every 500 microseconds the Z2 interrupts what it is
doing to perform periodic tasks such as updating sensor inputs values and checking for the occurrence of a crank position pulse. If this pulse is
observed, a program known as the decision maker is executed and performs high priority tasks such as fuel and spark calculations, and RPM
processing. Low priority tasks (i.e. OBDII processing, SCI and CCD communications) are executed during the time between crank pulses.
The Z2 software is divided into a main operating strategy and three separate calibration areas. The main strategy contains information specific to
the various engines and transmissions supported by this PCM. Once installed, the information contained in this area is fixed for a given engine and
transmission. Changes to this data, if required, can be performed only by computer programming personnel. The calibration areas (engine,
transmission and OBDII) contain information relating to emissions, fuel economy and driveability and can be altered directly by calibration
personnel.
