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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Keyboard Interface of The keyboard matrix can be any size from 2×2 to 8×8. To determine if a character has been typed, the FIFO status register is checked. MMM sets keyboard mode.

Z selects auto-increment for the address. 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. Each counter has a program control word used to select the way the counter operates. Strobed keyboard, decoded display scan.

Microprocessor – I/O Interfacing Overview

Selects type of write and the address of the write. The previous example illustrates an encoded keyboard, external decoder used to drive matrix.


Shift connects to Shift key on keyboard. Encoded keyboard with N-key rollover.

Microprocessor I/O Interfacing Overview

Selects type of FIFO read and address of the read. Usually decoded at port address 40HH and has following functions: The scans RL pins synchronously with the scan. The output becomes a logic 0 when the control word is written and remains there until N plus the number of programmed counts. Selects 8122 number of display positions, type of key scan Generates a continuous square-wave with G set to 1.

An events counter enabled with G. 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.

Encoded keyboard with 2-key lockout. 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: Controls up to a digit numerical display.

There are 6 modes of operation for each counter: Interface of Code given in text for reading keyboard. Scans and encodes up to a key keyboard. The display is controlled from an 82122 16×8 RAM that stores the coded display information. Generates a basic timer interrupt that occurs at approximately Causes DRAM memory system to be refreshed. Programs internal clk, sets scan and debounce times.


The 74LS drives 0’s on one line at a time. Chip select that enables programming, reading the keyboard, etc.

Programmable Keyboard/Display Interface –

Clears the IRQ signal to the microprocessor. Used for controlling real-time events such as real-time clock, events counter, and motor speed and direction control. Consists of bidirectional pins that connect to data bus on micro. Pinout Definition A0: DD Function 00 8-digit display with left entry 01 digit display with left entry 10 8-digit display with right entry intrefacing digit display with right entry.

Once done, a procedure is needed to read data from the keyboard.

Scan line outputs scan both the keyboard and displays. Allows half-bytes to be blanked. Unlike the 82C55, the must be programmed first. Keyboard Interface of MMM field: Six Digit Display Interface of DD field selects either: Pins SL2-SL0 sequentially scan each column through a counting operation.

Counter reloaded if Intertacing is pulsed again. Keyboard Interface of Interrupt request, becomes 1 when a key is pressed, data is available.

Sl outputs are active-high, follow binary bit pattern or Provides a timing source to the internal speaker and other devices. Used internally for timing.