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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The 74LS drives 0’s on one line at a time.

BB works similarly except that they blank turn off half of the output pins. Keyboard Interface of MMM field: RL pins incorporate internal pull-ups, no need for external resistor pull-ups.

Keyboard has a built-in FIFO 8 character buffer. Generates a basic timer interrupt that occurs at approximately Minimum count is 1 all modes except 2 and 3 with minimum count of 2. Scans and encodes up to a key keyboard.


Microprocessor – I/O Interfacing Overview

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. The scans RL pins synchronously with the scan. Shift connects to Shift key on keyboard. Once done, a procedure is needed to read data from the keyboard. The address inputs select one of the four internal registers with the as follows: The first 3 bits of sent to control port selects one of 8 control words.

Microprocessor I/O Interfacing Overview

8122 lines are inputs used to sense key depression in the keyboard matrix. The output becomes a logic 0 when the control word is written and remains there until N plus the number of programmed counts. MMM sets keyboard mode. 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. Counter interfacjng if G is pulsed again.

Provides a timing source to the internal speaker and other devices. Programs internal clk, sets scan and debounce times. Selects the number of display positions, type of key scan To determine if a character has been typed, the FIFO status register is checked.


Interrupt request, becomes 1 when a key is pressed, data is available. Keyboard Interface of Causes DRAM memory system to be refreshed.

Interface of Code given in text for reading keyboard. Keyboard Interface of The keyboard matrix can be any size from 2×2 to 8×8.

Used for controlling real-time events such as real-time clock, events counter, and motor speed and direction control. Keyboard Interface of First three bits given below select one intterfacing 8 control registers opcode.

Programmable Keyboard/Display Interface –

Chip select that enables programming, reading the keyboard, etc. Interface of 2 Keyboard type is programmed next. Usually decoded at port address 40HH and has following functions: Unlike the 82C55, the must be programmed first. Controls up to a digit numerical display.