I/O interfacing circuits –Hand shaking,serial and parallel interfacing – Address decoding Interfacing chips Programmable peripheral interfacing. In this presentation we get to know about keyboard Features, Cpu interface pins, Key board Data, Display data, Timing and control. Intel Programmable Key Board/Display Interface is available in the The description of pins of Programmable keyboard/display interface is given.
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Usually decoded at port address 40HH and has following functions: This unit first scans the key closure row-wise, if found then the keyboard debounce unit debounces the key entry. Keyboard has a built-in FIFO 8 character buffer.
There are 6 modes of operation for each counter: The 74LS drives 0’s on one line at a time. It has an internal pull inetrface.
Intel – Wikipedia
DD Function Encoded keyboard with keygoard 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: 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.
Selects type of display read and address of the ieyboard. 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.
In the decoded scan modethe counter internally intetface the least significant 2 bits and provides a decoded 1 out of 4 scan on SL 0 -SL 3. Keyboard Interface of The keyboard matrix can be any size from 2×2 to 8×8. Strobed keyboard, encoded display inetrface. These lines can be programmed as encoded or decoded, using the mode control register.
Interface of 2 Keyboard type is programmed next. An events counter enabled with G. Its data buffer interfaces the external bus of the system with the internal bus of the microprocessor.
Programmable Keyboard/Display Interface –
Pins SL2-SL0 sequentially scan each column through a counting operation. Encoded keyboard with 2-key lockout.
Shift interfcae to Shift key on keyboard. The Shift input line status is stored along with every key code in FIFO in the scanned keyboard mode. Keyboard Interface of MMM field: The display is controlled from an internal 16×8 RAM that stores the coded display information.
In the Polled modethe CPU periodically reads an internal flag of to check whether any key is pressed or not with key pressure. Generates a continuous square-wave with G set to 1. Causes DRAM memory system to be refreshed.
Pinout Definition A0: Each counter has a program control word used to select the way the counter operates.
These are the scan lines used to scan the keyboard matrix and display the digits. In the scanned sensor matrix mode, this unit acts as sensor RAM where its each row is loaded with the status of their corresponding row of sensors into the matrix.
Selects the number of display positions, type of key scan RL pins incorporate internal pull-ups, no need for external diaplay pull-ups. Keyboard Interface of First three bits given below select one of 8 control registers opcode. 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.
Counter reloaded if G is pulsed again. This mode is further classified into two output modes. Keyboard Interface of