Intel Microcontroller I/O Ports Overview, Bidirectional Ports, Device I/O Ports, Port Bits Type

CHAPTER 7

I/O PORTS

I/O ports provide a mechanism to transfer information between the device and the surrounding system circuitry. They can read system status, monitor system operation, output device status, configure system options, generate control signals, provide serial communication, and so on. Their usefulness in an application is limited only by the number of I/O pins available and the imagination of the engineer.

7.1I/O PORTS OVERVIEW

Standard I/O port registers are located in the SFR address space and they can be windowed. Mem- ory-mapped I/O port registers are located in memory-mapped address space. Memory-mapped registers must be accessed with indirect or indexed addressing; they cannot be windowed. All ports can provide low-speed input/output pins or serve alternate functions. Table 7-1 provides an overview of the device I/O ports. The remainder of this chapter describes the ports in more detail and explains how to configure the pins. The chapters that cover the associated peripherals discuss using the pins for their special functions.

		Table 7-1.	Device I/O Ports
Port	Bits	Type		Direction	Associated Peripheral(s)
Port 1	8	Standard		Bidirectional	EPA and timers
Port 2	8	Standard		Bidirectional	SIO, interrupts, bus control, clock gen.
Port 3	8	Standard		Bidirectional	Chip-select unit, interrupts
Port 4	4	Standard		Bidirectional	PWM
EPORT	4	Memory mapped (NP)		Bidirectional	Extended address lines
		Standard (NU)

7.2BIDIRECTIONAL PORTS 1–4

The bidirectional ports are very similar in both circuitry and configuration. All ports use Schmitt- triggered input buffers for improved noise immunity. Table 7-2 lists the bidirectional port pins with their special-function signals and associated peripherals.

7-1