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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Selects the number of display positions, type of key scan Programs internal clk, sets scan and debounce times. Selects type of FIFO read and address of the read. Selects type of display read and address of the read.

Selects type of write and the address of the write. Scans and encodes up to a key keyboard. Controls up to a digit numerical display. Keyboard has intercacing built-in FIFO 8 character buffer. The display is controlled from an internal 16×8 RAM that stores the coded display information.

Pinout Definition A0: Output that blanks the displays. Used internally for timing. Max jnterfacing 3 MHz. Chip select that enables programming, reading the keyboard, etc. Consists of bidirectional pins that connect to data bus on micro.

Interrupt request, becomes 1 when a key is pressed, data is available. Return lines are inputs used to sense key inetrfacing in the keyboard matrix. Shift connects to Shift key on keyboard. Scan line outputs scan both the keyboard and displays. Keyboard Interface of Keyboard Interface of The keyboard matrix can be any size from 2×2 to 8×8.


Pins SL2-SL0 sequentially cuip each column through a counting operation. The 74LS drives 0’s on one line at a time.

Microprocessor – I/O Interfacing Overview

The scans RL pins synchronously with the scan. RL interfacinf incorporate internal pull-ups, no need for external resistor pull-ups. Unlike the 82C55, the must be programmed first.

The first 3 bits of sent to control port selects one of 8 control words. Keyboard Interface of First three bits given below select one of 8 control registers opcode. DD sets displays mode.

MMM sets keyboard mode. DD field selects either: 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. Keyboard Interface of MMM field: DD Function Encoded keyboard with 2-key lockout Decoded keyboard with 2-key lockout Encoded keyboard with N-key rollover Decoded keyboard with N-key rollover Encoded sensor matrix Decoded sensor matrix Strobed keyboard, encoded display scan Strobed keyboard, decoded display scan Encoded: Sl outputs are active-high, follow interfacong bit pattern or SL outputs are active-low only one low at any time.

Z selects auto-increment for the address.

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. BB works similarly except that they blank turn off half of the output pins.

Interface of 2 Keyboard type is programmed next. The previous example illustrates an encoded keyboard, external decoder used to drive matrix. Once done, a procedure is needed to read data from the keyboard. To determine if a character has been typed, the FIFO status register is checked. Interface of Code given in text for reading keyboard. Six Digit Display Interface of Used for controlling real-time events such as real-time clock, events counter, and motor speed and direction control.


Usually decoded at port address 40HH and has following functions: Generates a basic timer interrupt that occurs at approximately Intterfacing the micro at interrupt vector 8 for a clock tick. Causes DRAM memory system to be refreshed. Provides a timing source to the internal speaker and other devices. The address inputs select one of the four internal registers with the as follows: Minimum count is 1 all modes except 2 and 3 with minimum count of 2.

Each counter has a program control word used to select the way the counter operates. 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. There are 6 modes of operation for each counter: An events counter enabled with G. The output becomes a logic 0 when the control word is written and remains there until N plus the number of programmed counts.

Counter reloaded if G is pulsed again. Generates a continuous square-wave with G set to 1. Allows half-bytes to be blanked. Clears the display or FIFO. Clears the IRQ signal to the inerfacing. Encoded keyboard with 2-key lockout. Decoded keyboard with 2-key lockout.

Programmable Keyboard/Display Interface –

Encoded keyboard with N-key rollover. Decoded keyboard with N-key rollover. Strobed keyboard, encoded display scan. Strobed keyboard, decoded display scan.