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. Usually decoded at port address 40HH and has following functions: Onterfacing keyboard, decoded display scan.

Microprocessor – I/O Interfacing Overview

Minimum count is 1 all modes except 2 and 3 with minimum count of 2. Interrupts the micro at interrupt vector 8 dhip a clock tick.

Pins SL2-SL0 sequentially scan each column through a counting operation. DD field selects either: Encoded keyboard with N-key rollover. Used for controlling real-time events such as real-time clock, events counter, and motor speed and direction control.

Selects type of display read and address of the read. Unlike the 82C55, the must be programmed first. Sl outputs are active-high, follow binary bit pattern or 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. Programs internal clk, sets scan and debounce times. The output becomes a logic 0 when the control word is written and remains there until N plus the number of programmed counts.


Max is 3 MHz. Allows half-bytes to be blanked. MMM sets keyboard mode. Clears the display or FIFO. The 74LS drives 0’s on one line at a time.

Programmable Keyboard/Display Interface –

Each counter has a program control word used to select the way the counter operates. Once done, a procedure is needed to read data from the keyboard. Pinout Definition A0: The first 3 bits of sent to ingerfacing port selects one of 8 control words. There are 6 modes of operation for each counter: Provides a timing source to the internal speaker and other devices. Selects type of write and the address of the write. Selects type of FIFO read and address of the read.

The address inputs select one of the four internal registers with the as follows: Clears the IRQ signal to the microprocessor. Decoded keyboard with N-key rollover. Keyboard Interface of First three bits given below select one of 8 control registers opcode. Keyboard Interface of Causes DRAM memory system to be refreshed.

interfaing Chip select that enables programming, reading the keyboard, etc. Decoded keyboard with 2-key lockout. Output that blanks the displays. DD Function 00 8-digit display with left entry 01 digit display with left 82212 10 8-digit display with right entry 11 digit display with right entry.


Generates a basic timer interrupt that occurs at approximately The scans RL pins synchronously with the scan. To determine if a character has been typed, the FIFO status register is checked.

Strobed keyboard, encoded display scan. Shift connects to Shift key on keyboard.

SL outputs are active-low only one low at any time. The previous example illustrates an encoded keyboard, external decoder used to drive matrix. RL pins incorporate internal pull-ups, no need for external resistor pull-ups. 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: Consists of bidirectional pins that connect to data bus on micro.

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 display is controlled from an internal 16×8 RAM that stores the coded display information. Keyboard Interface of MMM field: