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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Programs internal clk, sets scan and debounce times. Strobed keyboard, encoded display scan.

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. Controls up to a digit numerical display. The interfacng drives 0’s on one line at a time. 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.

Pinout Definition Innterfacing Allows half-bytes to be blanked.

Clears the IRQ signal to the microprocessor. Keyboard has a built-in FIFO 8 character buffer. RL pins incorporate internal pull-ups, no need for external resistor pull-ups. The scans RL pins synchronously with the scan. BB works similarly except that they blank turn off half of the output pins. Interface of Code given in text for reading keyboard. Decoded keyboard with 2-key lockout.


There are 6 modes of operation for each counter: Selects type of display read and address of the read. Provides a timing source to the internal speaker and other devices. Consists of bidirectional pins that connect to data bus on micro. The previous example illustrates an encoded keyboard, external decoder used to drive matrix.

Microprocessor – I/O Interfacing Overview

Scans and encodes up to a key keyboard. Keyboard Interface of First three bits given below select one of 8 control registers iinterfacing. Clears the interfaxing or FIFO. Used for controlling real-time events such as real-time clock, events counter, and motor speed and direction control. Keyboard Interface of Scan line outputs scan both the keyboard and displays.

SL outputs are active-low only one low at any time. DD sets displays mode. Selects type of FIFO read and address of the read. Return lines are inputs used to sense key depression in the keyboard matrix.

Each counter has a program control word used to select the way the counter operates. MMM sets keyboard mode.

Sl outputs are active-high, follow binary bit pattern or The display is controlled from an internal 16×8 RAM that stores the coded display information. Interface of 2 Keyboard type is programmed next. Encoded keyboard with N-key rollover. Output that blanks the displays. 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.


Interrupts the micro at interrupt vector 8 for a clock tick. Selects the number of display positions, type of key scan Interrupt request, becomes 1 when a key is pressed, data is available. Pins SL2-SL0 sequentially scan each column through a counting operation. 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. Max is 3 MHz. DD field selects either: Decoded keyboard with N-key rollover. Encoded keyboard with 2-key lockout. Chip select that enables programming, reading the keyboard, etc. Keyboard Interface of The keyboard matrix can be any size from 2×2 to 8×8.

Programmable Keyboard/Display Interface –

Selects type of write and the address of the write. Used internally for timing. Strobed keyboard, decoded display scan. Usually decoded at port address 40HH and has following functions: