Intel 8XC196NT, Руководство пользователя

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6-1
CHAPTER 6
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.
6.1 I/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 6-1 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.
6.2 INPUT-ONLY PORT 0
Port 0 is a four-bit, high-impedance, input-only port. Its pins can be read as digital inputs; they
are also inputs to the A/D converter. Port 0 differs from the other ports in that its pins can be used
only as inputs to the digital or analog circuitry.
Because port 0 is permanently configured as an input-only port, it has no configuration registers.
Its single register, P0_PIN, can be read to determine the current state of the pin. The register is
byte-addressable and can be windowed. (See “Windowing” on page 4-15)
Table 6-1. Device I/O Ports
Port Bits Type Direction Associated Peripheral(s)
Port 0 4 Standard Input-only A/D converter
Port 1 8 Standard Bidirectional EPA and timers
Port 2 8 Standard Bidirectional SIO, interrupts, bus control, clock gen.
Port 3 8 Memory-mapped Bidirectional Address/data bus
Port 4 8 Memory-mapped Bidirectional Address/data bus
Port 5 8 Memory-mapped Bidirectional Bus control, slave port
Port 6 8 Standard Bidirectional EPA, SSIO
EPORT 4 Memory-mapped Bidirectional Extended address lines