The family was designed using software that compiles a computer language into hardware. The submodules of the microcontroller were designed independently and released as new CPUs could be tested.
This process let the architects perform "design-ahead" so that when silicon technlogies were available, Motorola had designs ready to implement and go to market.
The microcontrollers consist of a series of parts, connected by an internal bus:
The CPU, designed to minimize transistors while maximizing performance.
The CPU has a high-speed clocked serial debugger interface called "background debug mode." The 68300-series was the first to have a clocked serial interface to the CPU to perform debugging. Now, many CPUs use a standard serial test interface for this purpose.
The SIM (System Interface Module), which eliminates much "glue logic" by decoding addresses into control signals. It also provides a clock generator, watchdogs for various system operations, access to most processor pins as parallel ports, and a periodic timer. It also provides an interrupt controller.
The Timing Processor Unit (TPU), which performs almost any timing related task: timers, counters, proportional pulse width control, pulse width measurement, pulse generation, stepper motor controllers, quadrature detection, etc.
An auxiliary RAM doubles as a programmable microcontroller store for the TPU, and Motorola gives the development system and code away for free.
Some earlier models have two conventional counter-timers.
Some models have a network interface processor.
Most models has a "serial peripheral interface", a clocked serial interface that can rapidly load bits into an external device.
Most models have a serial UART.