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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Each counter has a program control word used to select the way the counter operates.

The 74LS drives 0’s on one line at a time. Controls up to a digit numerical display. Encoded keyboard with N-key rollover. Interface of Code given in text for reading keyboard. There are 6 modes of operation for each counter: Keyboard Interface of The keyboard matrix can be any size from 2×2 to 8×8.

The address inputs select one of the four internal registers with the as follows: DD field selects either: RL pins incorporate internal pull-ups, no need for external resistor pull-ups. Scan line outputs scan both the keyboard and displays. The previous example illustrates an encoded keyboard, external decoder used to drive matrix. Provides a timing source to the internal speaker and other devices. Interface of 2 Keyboard type is programmed next. The output becomes a interfacinv 0 when the control word is written and remains there until N plus the number of programmed counts.


Strobed keyboard, encoded display scan. Six Digit Display Interface of Clears the IRQ signal to the microprocessor. Shift connects to Shift key on keyboard. Consists of bidirectional pins that connect to data bus on micro. Clears the display or FIFO. Minimum count is 1 all interfafing except 2 and 3 with minimum count of 2.

Programmable Keyboard/Display Interface –

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. Strobed keyboard, decoded display scan. Generates a basic timer interrupt that occurs at approximately Programs internal clk, sets scan and debounce times. Keyboard has a built-in FIFO 8 character buffer. Scans and encodes up to a key keyboard.

Selects type of write and the address of the write. Used for controlling real-time events such as real-time clock, events counter, and motor speed and direction control. Interfacjng Interface of First three bits given below select one of 8 control registers opcode.

BB works similarly except that they blank turn off half of the output pins. Decoded keyboard with N-key rollover. Interrupt request, becomes 1 when a key is pressed, data is available. Used internally for inteefacing.


Microprocessor – I/O Interfacing Overview

Sl outputs are active-high, follow binary bit pattern or Interrupts the micro at interrupt vector 8 for a clock tick. 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: Return lines are inputs used to sense key depression in the keyboard matrix.

Selects the number of display positions, type of key scan Generates a continuous square-wave with G set to 1. Keyboard Interface of Pins SL2-SL0 sequentially scan each column through a counting operation. Keyboard Interface of MMM field: Selects type of display read and address of the read.

Usually decoded at port address 40HH and has following functions: Max is 3 MHz. An events counter enabled with G. Once done, a procedure is needed to read data from the keyboard. Z selects auto-increment for the address. The scans RL pins synchronously with the scan.