Microprocessor Systems
All microprocessor systems perform the same essential functions, that is, data or signal input, storage, processing and output. However, the PC is a relatively complex microprocessor system, with a hierarchical bus structure, which has developed to improve system performance by alleviating the bus bottleneck of earlier designs. The Intel PC processor itself also has many additional performance-enhancing features such as cache memory, multiple processing pipelines and multiple cores. To understand the microcontroller, we need to go back to a simpler system.
The basic microprocessor system needs a certain set of chips, with suitable interconnections, as follows:
• CPU
• RAM
• ROM
• I/O ports.
These devices must be interconnected by:
• Address bus
• Data bus
• Various control lines.
These buses and control lines originate from the CPU, which is in charge of the system. RAM and ROM chips are usually general purpose hardware, which can be used in any system. The I/O chips are sometimes designed to work with a particular processor, but all provide specific interfacing functions. In a basic system, this would be simple digital input and output, with perhaps a serial port providing an RS232 (see Chapter 12) type data link.
Additional support chips are needed to make a CPU system work. In a minimal system, an address decoder is needed to select the memory chip or I/O device required for a data transfer to or from the CPU. This system is illustrated in Figure 1.6a, and there is further information about microprocessor system operation in Chapter 14 and Appendix C.