Data Sheet

UCTRONICS Ultimate Starter Leaning Kit for Raspberry Pi #K0064
99 www.uctronics.com
A 8x8 dot-matrix display consists of 64 LEDs, and each LED is placed at the intersection of
the lines and columns. When the corresponding row is set as high level and the column is set
as low level, then the LED will be lit.
A certain drive current is required for the dot-matrix display. In addition, more pins are
needed for connecting dot-matrix display with controller. Thus, to save the Raspberry Pi
’
s
GPIO, driver IC 74HC595 is used in this experiment.
3. What
’
s 74HC595 ?
The 74HC595 is an 8-stage serial shift register with a storage register and 3-state outputs.
The shift register and storage register have separate clocks. Data is shifted on the
positive-going transitions of the SH_CP input. The data in each register is transferred to the
storage register on a positive-going transition of the ST_CP input. The shift register has a
serial input (DS) and a serial standard output (Q7
’
) for cascading. It is also provided with
asynchronous reset (active LOW) for all 8 shift register stages. The storage register has 8
parallel 3-state bus driver outputs. Data in the storage register appears at the output
whenever the output enable input (OE) is LOW.
In this experiment, only 3 pins of Raspberry Pi are used for controlling a dot-matrix display
due to the existence of 74HC595.
The flowing is the function of each pin:
DS: Serial data input
Q0-Q7: 8-bit parallel data output
Q7: Series data output pin, always connected to DS pin of the next 74HC595
OE: Output enable pin, effective at low level, connected to the ground directly