CHAPTER 11

Variable address

The 16-bit I/O address in DX is called

Fixed address

Intel calls the 8-bit form (p8) a__because it is stored with the instruction, usually in a ROM

Port number (or simply port

Whenever data are transferred by using the IN or OUT instructions,

the I/O address, often called a

Isolated I/O

the IN, INS, OUT, and OUTS instructions transfer data between the

microprocessor's accumulator or memory and the I/O device

Memory-mapped I/O

any instruction that references memory can accomplish the

transfer

Isolated

describes how the I/O locations are isolated from the memory

system in a separate I/O address space

Basic input device

Is a set of three-state buffers

handshaking or polling

Another method of I/O control, called__synchronizes the I/O

device with the microprocessor

Programmable peripheral interface (PPI

is a very popular, low-cost interfacing component found in many applications

Stepper motor

is a digital motor because it is moved in discrete steps as it traverses through 360

Bidirectional bus

is used by referencing port A with the IN and OUT instructions

modem

which is a device that converts TTL levels of serial data into audio tones that can pass through the telephone system

16550

programmable communications interface, capable of receiving and transmitting

asynchronous serial data

DAC0830

is an 8-bit digital-to-analog converter that converts a digital signal to an analog voltage within 1.0 µs

ADC0804

is an 8-bit analog-to-digital converter that converts an analog signal into a digital signal within 100 με

strobe

input loads data into the port latch, which holds the information until it is input to the microprocessor via the IN instruction.

Input buffer full (IBF)

is an output indicating that the input latch contains information

Interrupt request

pin becomes a logic 1 when the STB input returns to a logic 1, and is cleared when the data are input from the port by the microprocessor.

interrupt

enable signal is neither an input nor an output; it is an internal bit programmed via the port PC4 (port A) or PC2 (port B) bit position.

Output buffer full (obf)

This signal is set to a logic 1 whenever the ack pulse returns from the external device.

acknowledge signal

signal is a response from an external device, indicating that it has received the data from the 82C55 port.

Interrupt request

is an output used to interrupt the microprocessor for both input and output conditions.

clock

input is the timing source for each of the internal counters.

Chip select

enables the 8254 for programming and reading or writing a counter

counter outpu

is where the waveform generated by the timer is available.

MODE0

the output becomes a logic 0 when the control word is written and remains there until N plus the number of programmed counts.

MODE 1

Causes the counter to function as a retriggerable, monostable multivibrator (one-shot).

MODE 2

Allows the counter to generate a series of continuous pulses that are one clock pulse wide

MODE 3

Generates a continuous square wave at the OUT connection, provided that the G pin is a logic 1.

MODE 4

Allows the counter to produce a single pulse at the output. If the count is programmed as a 10, the output is high for 10 clocking periods and low for one clocking period.

MODE 5

A hardware triggered one-shot that functions as mode 4, except that it is started by a trigger pulse on the G pin instead of by software.

address strobe

input is used to latch the address lines and chip select lines

baud out

pin is where the clock signal generated by the baud rate gen erator from the transmitter section is made available.

clear-to-send

This pin is often used in a half-duplex system to turn the line around

data carrier detect

input is used by the modem to signal the 16550 that a carrier is present.