Explain keyboard interfacing to 8088 through 8279.

The 8279 is a programmable keyboard and display interfacing component which scans and encodes up to a 64-key keyboard and controls up to a sixteen-digit numerical display.

The keyboard interface has built in first-in first-out (FIFO) buffer which allows this store up to eight keystrokes before the microprocessor should retrieve a character. The display section controls up to sixteen numeric displays from an internal 16 X 8 RAM which stores the coded display information.

The keyboard section has eight lines that can be connected to eight columns of a keyboard, in addition two additional lines including shifting and CNTL/STB keys. The key pressed are automatically de-bounced and the keyboard can operate into two modes two as: key lock out or n-key rollover. When two keys in the two as key lock out mode are pressed concurrently, only first key is known. In the N-key roll over mode, simultaneous key are known and their codes are stored into the internal buffer.

Control Word: 000DDMMM - Mode set is command with an op-code of 000 and two fields programmed to choose the mode of operation for the 8279. The DD field chooses the mode of operation for the display and the MMM field decides the mode of operation for the keyboard.  

The 8279 control word summary

Posted Date: 5/25/2013 8:45:00 AM | Location : United States

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