Designing Embedded Hardware

A Simple 68000-Based Computer

Let’s look now at a small 68000-based computer. For simplicity, we’ll give it just a small amount of memory and a single peripheral, an MK68901 MFP (Multifunction Peripheral) produced by ST Electronics. The MFP gives us a UART (covered in detail in Chapter 10), parallel I/O, and interrupt control. A block diagram of the system is shown in Figure 7-4.

Figure 7-4. A 68000-based computer

This system is designed with only a small amount of memory, so as to keep the design uncomplicated. While this is not much compared to many desktop machines, it is sufficient for many small control applications.

This design could be used for a number of simple applications. The counters of the MK68901 may be used to monitor external event pulses or to generate PWM for motor control. (We’ll see how to do that in Chapter 12.) This computer could also be used to accept commands through its serial port and activate (or deactivate) external subsystems using the parallel I/O pins of the MK68901. This basic design could also be adapted to provide a bridge between an RS-232C interface (Chapter 10) and a parallel port. You could use this to interface a parallel-port printer to a serial-port-only computer. Alternatively, you could use it to put a serial modem on your PC’s parallel port. Using the bus-interfacing techniques we learned in Chapter 6, you could add additional peripherals ...