Description: The NTE input/output port is an integrated circuit in a 24–Lead DIP type package and consists of an 8–bit latch with three–state output buffers. Computer interfacing has traditionally been an art, the art to design and implement the Microprocessor interface-chips have not reached their maturity yet. They are still “dumb” chips. System Controller Using and ‘s. Control or. After a delay, call it to/-, chip 1 data outputs again enter the float state. Example In Example , we developed a decoding circuit for interfacing EPROM within the memory chips, we have used the latch in Fig to latch this byte.

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82212 Chip select that enables programming, reading the keyboard, etc. Interface of 2 Keyboard type is programmed next. DD sets displays mode. Encoded keyboard with 2-key lockout. Each counter has a program control word used to select the way the counter operates. Interface of Code given in text for reading keyboard.

Microprocessor I/O Interfacing Overview

BB works similarly except that they blank turn off half of the output pins. The scans RL pins synchronously with the scan.

Allows half-bytes to be blanked. DD Function 00 8-digit display with left entry 01 digit display with left entry 10 8-digit display with right entry 11 digit display with right entry. If two bytes are programmed, then the first byte LSB stops the count, and the second byte MSB starts the counter with the new count. Six Digit Display Interface of The output becomes a logic 0 when the control word is written and remains there until N plus the number of programmed counts.


The address inputs select one of the four internal registers with the as follows: Pins SL2-SL0 sequentially scan each column through a counting operation.

Provides a timing source to the internal speaker and other devices. SL outputs are active-low only one low at any time.

Keyboard Interface of The keyboard matrix can be any size from 2×2 to 8×8. Once done, a procedure is needed to read data from the keyboard. Clears the display or FIFO. Generates a basic timer interrupt that occurs at approximately Return lines are inputs used to sense key depression in the keyboard matrix. DD field selects either: Generates a continuous square-wave with G set to 1. Selects type of write and the address of inferfacing write.

Pinout Definition A0: Controls up to a digit numerical interfaciing. To determine if a character has been typed, the FIFO status register is checked. Sl outputs are active-high, follow binary bit pattern or The first 3 bits of sent to control port selects iterfacing of 8 control words.

Microprocessor – I/O Interfacing Overview

Keyboard Interface of Selects the number of display positions, type of interffacing scan Output that blanks the displays. Clears the IRQ signal to the microprocessor. Interface of WWBB The display write inhibit control word inhibits writing to either the leftmost 4 bits of the display left W or rightmost 4 bits. Keyboard has a built-in FIFO 8 character buffer. Used internally for timing.


Interrupts the micro at interrupt vector 8 for a clock tick. Usually decoded at port address 40HH and has following functions: Used for controlling real-time events such as real-time clock, events counter, and motor speed and direction control.

Scans and encodes up to a key keyboard. Interrupt request, becomes 1 when a key is pressed, data is available.

Programmable Keyboard/Display Interface –

Consists of bidirectional pins that connect to data bus on micro. Strobed keyboard, encoded display scan. Strobed keyboard, decoded display scan. Unlike the 82C55, the must be programmed first. The previous example illustrates an encoded keyboard, external decoder used to drive matrix.

Z selects auto-increment for the address. An events counter enabled with G. Max is 3 MHz. Counter reloaded if G 822 pulsed again.

Selects type of FIFO read and address of the read. RL pins incorporate internal pull-ups, no need for external resistor pull-ups. There are 6 modes of operation for each counter: