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181 Chapter 17 74HC595 & LEDBar Graph █ www.freenove.com
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Component knowledge
74HC595
74HC595 chip is used to convert serial data into parallel data. 74HC595 can convert the serial data of one
byte to 8 bits, and send its corresponding level to the corresponding 8 ports. With this feature, 74HC595 can
be used to expand the IO port of Arduino board. At least 3 ports on the RPI board are need to control 8 ports
of 74HC595.
The ports of 74HC595 are described as follows:
Pin name Pin number Description
Q0-Q7 15, 1-7 Parallel data output
VCC 16 The positive electrode of power supply, the voltage is 2~6V
GND 8 The negative electrode of power supply
DS 14 Serial data Input
OE 13 Enable output,
When this pin is in high level, Q0-Q7 is in high resistance state
When this pin is in low level, Q0-Q7 is in output mode
ST_CP 12 Parallel update output: when its electrical level is rising, it will update the
parallel data output.
SH_CP 11 Serial shift clock: when its electrical level is rising, serial data input register will
do a shift.
MR 10 Remove shift register: When this pin is in low level, the content in shift register
will be cleared .
Q7' 9 Serial data output: it can be connected to more 74HC595 in series.
For more detail, please refer to the datasheet.