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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Scan line outputs scan both the keyboard and displays.

Microprocessor – I/O Interfacing Overview

Z selects auto-increment for the address. 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.

RL pins incorporate internal pull-ups, no need for external resistor pull-ups. Keyboard has a built-in FIFO 8 character buffer. SL outputs are active-low only one low at any time. If two bytes are programmed, then the first byte LSB 2812 the count, and the second byte MSB starts the counter with the new count. Selects type of display read and address of the read.


Microprocessor I/O Interfacing Overview

Usually decoded at port address 40HH and has following functions: DD field selects either: Interrupt request, becomes 1 when a key is pressed, data is available. Max is 3 MHz. BB works similarly except that they blank turn off half of the output pins.

Pinout Definition A0: The output becomes interfaxing logic 0 when the control word is written and remains there until N plus the number of programmed counts. Generates a continuous square-wave with G set to 1. Used for controlling real-time events such as real-time clock, events counter, and motor speed and direction control.

Programmable Keyboard/Display Interface –

Interface of Code given in text for interfackng keyboard. The scans RL pins synchronously with the scan. Keyboard Interface of The keyboard matrix can be any size from 2×2 to 8×8. Used internally for timing. The first 3 bits of sent to control port selects one of 8 control words.

Scans and encodes up to a key keyboard.

Programs internal clk, sets scan and debounce times. Each counter has a program control word used to select the way the counter operates. Strobed keyboard, decoded display scan. Allows half-bytes to be blanked.


Shift connects to Shift key on keyboard. Output that blanks the displays. Sl outputs are active-high, follow binary bit pattern or Keyboard Interface of First three bits given below select one of 8 control registers opcode.

Selects type of write and the address of the write. Decoded keyboard with N-key rollover. Encoded keyboard with 2-key lockout.

Clears the display or FIFO. Encoded keyboard with N-key rollover. Six Digit Display Interface of Counter reloaded if G is pulsed again. The previous example illustrates an encoded keyboard, external decoder used to drive matrix.

Decoded keyboard with 2-key lockout. Selects type of FIFO read and address of the read. Unlike the 82C55, the must be programmed first. DD sets displays mode. Interrupts the micro at interrupt vector 8 for a clock tick. Interface of 2 Keyboard type is programmed next. Pins SL2-SL0 sequentially scan each column through a counting operation. An events counter enabled with G.