pic18f2550 and a 74hc595 shift register

Sometimes in your projects you simply do not have enough I/O lines available, take for example a lot of the multiple LED examples, these use 8 outputs to control 8 LEDs via your PIC, that can restrict the amount of outputs you would have available to drive other devices. Instead of this we can use a shift register, in this case a 74HC595 and using 3 I/O pins we can control 8 LED’s, that’s a saving of 5 I/O pins for other uses.

You can use it to control 8 outputs at a time while only taking up a few pins on your microcontroller. You can link multiple registers together to extend your output even more. The 74HC595 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

Lets look at the 74HC595

595 pin diagram

This is a link to the 74HC595 datasheet

Schematic

In the schematic below we have only shown 3 sets of resistors and LEDs but you could easily populate all 8

pic18f2550 and 74hc595 shift register

Code

This was written in mikroC PRO for PIC compiler, no libraries were used

<pre>#define SHIFT_CLOCK PORTB.F2
#define SHIFT_LATCH PORTB.F1
#define SHIFT_DATA PORTB.F0

void shiftdata595(unsigned char _shiftdata)
{
unsigned int i;
unsigned char temp;
temp = _shiftdata;
i=8;
while (i&gt;0)
{
if (temp.F7==0)
{
SHIFT_DATA = 0;
}
else
{
SHIFT_DATA = 1;
}
temp = temp&lt;&lt;1;
SHIFT_CLOCK = 1;
Delay_us(1);
SHIFT_CLOCK = 0;
i--;
}
}

void latch595()
{
SHIFT_LATCH = 1;
Delay_us(1);
SHIFT_LATCH = 0;
}

void main()
{
PORTB=0;
TRISB=0;
while(1)
{
shiftdata595(1);
latch595();
delay_ms(2000);

shiftdata595(0x02);
latch595();
delay_ms(2000);

shiftdata595(0b00000100);
latch595();
delay_ms(2000);
}
}</pre>

Links
10PCS SN74HC595N

30pcs SN74HC595N 8 Bit Shift Register