The Microcontroller Idea Book - Jan Axelson's Lakeview Research

Chapter 6
Table 6-1. Popular peripheral interface chips.
8253/4Programmable Interval Timer
Three independent 16-bit counters, 6 modes, up to 10 Mhz
8255 Programmable Peripheral Interface
Three 8-bit I/O pins, 3 modes, direct bit set/reset ability
8256 Multifunction Microprocessor Support Controller
Asynchronous serial interface, baud rate generator, five 8-bit timer/counters, two 8-bit
I/O ports, 8-level interrupt controller, programmable system clock
8259 Programmable Interrupt Controller
Eight-level priority controller, programmable interrupt modes
8279 Programmable Keyboard/Display Interface
Scanned interfaces to 64-contact key matrix and 16-character display.
The 8255 Programmable Peripheral Interface
In addition to the inputs and outputs provided by U12 and U14, there are specialized
peripheral-interface chips that you can add to your system. Table 6-1 lists several examples.
One of the most popular of these is the 8255 programmable peripheral interface, or PPI.
Figure 6-5 shows the pinout, and Table 6-2 shows the pin functions. The chip adds 24 bits
of I/O, plus the option to use special control and handshaking signals to communicate with
peripherals.
Intel originally introduced the 8255 as a peripheral for its 8085 microprocessor, but it remains
a popular chip for use with 8052s and other computer chips. Manufacturers of compatible
chips include AMD, OKI, Toshiba, and NEC, which calls its chip the μPD71055.
If you use the 8255, you’ll want a copy of its data sheet, which more fully explains its abilities
and configuration options.
8255 Variants
You have a choice of the original NMOS 8255 or the CMOS 82C55. The CMOS version
usually costs a little more, but has some advantages. First, it has lower power consumption,
with supply currents of 10 milliamperes (10 microamperes in standby mode with CS=high),
compared to 120 milliamperes for the 8255.
98 The Microcontroller Idea Book