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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Microprocessor I/O Interfacing Overview

Each counter has a program control word used to select the way the counter operates. Controls interfacimg to a digit numerical display.

Return lines are inputs used to sense key depression in the keyboard matrix. Interrupt request, becomes 1 when a key is pressed, data is available. Unlike the 82C55, the must be programmed first. Keyboard has a built-in FIFO 8 character buffer. Encoded keyboard with 2-key lockout. Output that inerfacing the displays. Selects type of write and the address of the write. Minimum count is 1 all modes except 2 and 3 with minimum count of 2.


Counter reloaded if G is pulsed again. Selects type of FIFO read and address of the read. Allows half-bytes to be blanked.

Microprocessor – I/O Interfacing Overview

DD field selects either: Scan line outputs scan both interfacinv keyboard and displays. Used for controlling real-time events such as real-time clock, events counter, and motor speed and direction control.

82122 Pinout Definition A0: Decoded keyboard with 2-key lockout. Chip select that enables programming, reading the keyboard, etc. The output becomes a logic 0 when the control word is written and remains there until N plus the number of programmed counts. DD sets displays mode. Generates a basic timer interrupt that occurs at approximately BB works similarly except that they blank turn off half of the interfxcing pins.

Generates a continuous square-wave with G set to 1. Consists of bidirectional pins that connect to data bus on micro. Max is 3 MHz. An events counter enabled with G.

Encoded keyboard with N-key rollover. Keyboard Interface of MMM field: Shift connects to Shift key on keyboard. Interrupts the micro at interrupt vector 8 interfacihg a clock tick. Interface of 2 Keyboard type is programmed next. Z selects auto-increment for the address.


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

Programs internal clk, sets scan and debounce times. Causes DRAM memory system to be refreshed. RL pins incorporate internal pull-ups, no need for external resistor pull-ups.

Six Digit Display Interface of Interface of Code given in text for reading keyboard. To determine if a character has been typed, the FIFO status register is checked. Clears the display or FIFO. Selects the number of display positions, type of key scan Provides a timing source to the internal speaker and other devices. Scans and encodes up to a key keyboard.

There are 6 modes of chiip for each counter: Used internally for timing. 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.