The X 86 Microprocessors: Architecture, Programming and Interfacing (8086 to Pentium) 2nd Edition by Pearson

21-10

THE

x86 MICROPROCESSORS

This corresponds to a refresh rate of around 83 times per second, which is sufficient to

fool the eye into believing that all the digits are ON at the same time [The persistence of

human vision is (1/16) of a second (62.5 ms)].

21.5 | Hex Keyboard Interfacing

In Section 9.12, the principle of operation of a hex keyboard has been discussed. With

that background, here, we will go on to understanding how such a keyboard is interfaced

to 8051.

See the diagram of the hex keyboard. Fig. 21.8 is a 4 × 4 matrix keyboard connected

to the 8051. For our purpose, we will use two ports of the 8051: Port 2 as an output port

connected ...