Page 75 - Embedded Microprocessor Systems Real World Design

ports. Some port ICs include hardware handshaking that permits a port to be used
for interprocessor communication in multiprocessor systems. The processor can
control the direction of each port (sometimes to the bit level, depending on the
part) and all modes of operation. 1/0 port ICs are also called pmt expanders.

Interface ICs

These provide standard interfaces, such as SCSI, IEEE-488, asynchronous serial
I/O, Ethernet, or “Firewire.” Many of these parts handle more than one interface.
Some UARTs (universal asynchronous receiver/transmitters) , for example, can
handle multiple serial protocols, relieving the processor from the burden of
handling each received byte.

Interrupt Controllers

Interrupt controllers simplify adding interrupts to processors. We’ll discuss this in
more detail in Chapter 5.

IC Functions
In many cases, an IC may combine two or more functions. Table 2.1 is a brief list
of typical peripheral ICs designed for microprocessor I/O.
There are fewer peripheral ICs on the market now than there were a few years
ago. This is the result of several factors. First, shrinking die sizes and power dissi-
pation allow more features to be integrated onto the CPU chip itself. Second, the
increasing complexity and decreasing cost of programmable logic devices such
as CPLDs and FPGAs make it more attractive to put peripheral functions on
those parts.

Table 2.1
Typical Peripheral I/O ICs.
Part Function Family

Intel 82C54 Three timers All Intel processors
Intel 8259 Interrupt controller Intel processors
Intel 8255 Four I/O ports Intel processors
Zilog Z84C20 Two 8-bit ports Zilog processors
Zilog 28530 Serial communications Non-Zilog processors
Zilog 28536 Three I/O ports, timers Non-Zilog processors
Motorola 68230 Parallel I/O ports 68000 family
Philips SCN68681 Dual UART 68000 family
National LM628 DC motor controller Intel processors

Hardware Design 1 59