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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Sl outputs are active-high, follow binary bit pattern or Interrupts the micro at interrupt vector 8 for a clock tick. 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.

Microprocessor – I/O Interfacing Overview

Six Digit Display Interface of Interface of Code given in text for reading keyboard. Clears the display or FIFO. The output becomes a logic 0 when the control word is written and remains there until N plus the number of programmed counts. SL outputs are active-low only one low at any time.


Encoded keyboard with N-key rollover. Selects the number of display positions, type of key scan MMM sets keyboard mode.

Programs internal clk, sets scan and debounce times. DD Function 00 8-digit display with left entry 01 digit display with left entry 10 8-digit interfaacing with right entry 11 digit display with right entry.

Microprocessor I/O Interfacing Overview

Scans and encodes up to a key keyboard. Strobed keyboard, encoded display scan. 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. Interrupt request, becomes 1 chil a key is pressed, data is available.

To determine if a character has been typed, the FIFO status register is checked. Minimum count is 1 all modes except 2 and 3 with minimum count of 2. 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: Generates a basic timer interrupt that occurs at approximately Selects type of FIFO read and address of the read.


Keyboard Interface of First three bits given below select one of 8 control registers opcode. Clears the IRQ signal to the microprocessor.

Programmable Keyboard/Display Interface –

Selects type of display read and address of the read. Return lines are inputs used to sense key depression in the keyboard matrix. Decoded keyboard with 2-key lockout. The first 3 bits of sent to control port selects one of 8 control words.

Decoded keyboard with N-key rollover.

Provides a timing source to the internal speaker and other devices. Selects type of write and the address of the write.

The address inputs select one of the four internal registers with the as follows: Unlike the 82C55, the must be programmed first.