February 14, 2020

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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Used internally for timing. RL pins incorporate internal pull-ups, no need for external resistor pull-ups. Chip select that enables programming, reading the keyboard, etc. Used for controlling real-time events such as real-time clock, events counter, and motor speed and direction control.

Sl outputs are active-high, follow binary bit pattern or Each counter has a program control word used to select the way the counter operates. The scans RL pins synchronously with the scan.

Generates a basic timer interrupt that occurs at approximately Interface of 2 Keyboard type is programmed next. 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, lnterfacing display scan Strobed keyboard, decoded display scan Encoded: Z selects auto-increment for the address.


Interface chi; Code given in text for reading keyboard. Return lines are inputs used to sense key depression in the keyboard matrix.

Microprocessor – I/O Interfacing Overview

Generates a continuous square-wave with G set to 1. Once done, a procedure is needed to read data from the keyboard. Pins SL2-SL0 sequentially scan each column through a counting operation. Clears the display or FIFO.

Interrupts the micro at interrupt vector 8 for a clock tick. Provides a timing source to the internal speaker and other devices. Keyboard has a built-in FIFO 8 character buffer. Programs internal clk, sets scan and debounce times. Pinout Definition A0: There are 6 modes of operation for each counter: Clears the IRQ signal to the microprocessor.

Programmable Keyboard/Display Interface –

Keyboard Interface of Selects the number of display positions, type of key scan Keyboard Interface of The keyboard matrix can be any size from 2×2 to 8×8. Interrupt request, becomes 1 when a key is pressed, data is available. The output becomes a logic 0 when the control word is written and remains there until N plus the number of programmed counts. Output that blanks the displays. Shift connects to Shift key on keyboard.

Scan line outputs scan both the keyboard and displays. Consists of bidirectional pins that connect to data bus on micro. Dhip Digit Display Interface of Strobed keyboard, encoded display scan. Controls up to a digit numerical display.

Selects type of display read and address of the read. Minimum count is 1 all modes except 2 and 3 with minimum count of 2. Encoded keyboard with N-key rollover.


SL outputs are active-low only one low at any time. Encoded cip with 2-key lockout. DD Function 00 8-digit display with left entry 01 interfacnig display with left entry 10 8-digit display with right entry 11 digit display with right entry. The first 3 bits of sent to control port selects one of 8 intrfacing words.

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. 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. BB works similarly except that they blank turn off half of the output pins. Allows half-bytes to be blanked.

Selects type of FIFO read and address of the read. Unlike the 82C55, the must be programmed first.

Microprocessor I/O Interfacing Overview

The previous example illustrates an encoded keyboard, external decoder used to drive matrix. The 74LS drives 0’s on one line at a time. Scans and encodes up to a key keyboard. Strobed keyboard, decoded display scan. DD field selects either: Decoded keyboard with N-key rollover.

To determine if a character has been typed, the FIFO status register is checked. Keyboard Interface of First three bits given below select one of 8 control registers opcode.