10-04-2017, 09:24 PM
This tutorial shows you how to control 16 LEDs with just 3 control lines. We do this by daisy chaining 74HC595 shift registers
The 74HC595 shift register has an 8 bit storage register and an 8 bit shift register. Data is written to the shift register serially, then latched onto the storage register. The storage register then controls 8 output lines. The figure below shows the 74HC595 pinout.
Pin 14 (DS) is the Data pin. On some datasheets it is referred to as "SER".
When pin 11 (SH_CP or SRCLK on some datasheets) goes from Low to High the value of DS is stored into the shift register and the existing values of the register are shifted to make room for the new bit.
Pin 12 (ST_CP or RCLK on some datasheets) is held low whilst data is being written to the shift register. When it goes High the values of the shift register are latched to the storage register which are then outputted to pins Q0-Q7.
The timing diagram below demonstrates how you would set the Q0-Q7 output pins to 11000011, assuming starting values of 00000000.
