74hc595

[chandrika]

Hi friends,
I am Chandrika. I'm new to using 74595. In my project I have used pic
16F505 and four 74595 shift regs. One LED & 7 relays are connected to
each 74595. My problem is how can I shift data & how can I turn ON/OFF
the LED and relays. Please help me.

[triple_x]

hi,
there are numerous discussion on 74595 shift register (serial-parallel). u can search the forum.

btw, here I attached my modified version, I'm not sure if anyone has already implemented this method, if so pls excuse. the code as below:

[John P]

Note that the EXP_OUT_ENABLE in Triple_X's code doesn't go to the enable line of the 74595, but to the RCLK input (pin 12, in the DIP package). If you want an on/off control for all the 595's outputs, the enable line is on pin 13. Tie it low if you don't need that feature. And tie the clear input (pin 10) high.

The outputs of the 595 don't change until you send a highgoing transition into pin 12, and then they all change at once. The serial data input is compatible with SPI, by the way, if you ever wanted to try it.

[chandrika]

Hi friends,

Thanks for giving me reply for 74hc595, but my problem is I have pic16f505 and 4x74595s. I am connecting 3 push buttons to 3 pins of pic as inputs and 4 pins of pic connected to 4x74595's. I assume 4x74595's as 4 channels. When I am pressing a push button, channel change to one by one. My problem is how can I send same 1 byte data from pic 4 to 4x74595 or how can I load data into 4x74595 ? Please help me.

[FvM]

The HC595 needs at least 3 signals (clock, data, latch), thus four HC595 need to be series conncted to a 32-bit shift register, if you want to control them individually. If you actually want to send the same data to four devices, you can connect the control signals in parallel of ourse.

[John P]

The fact that you're talking about 4 pins of the PIC being needed to send data to 4 74595's gives me a bad feeling for how much you know about using the '595. You only need 3 pins, no matter how many '595 chips you're using! I think you should either study the data sheet for this chip, or get someone to explain exactly how to use it. The code posted by Triple_X looks right; that should give you an idea of what to do.

[Guest]

[quote="chandrika"]Hi friends,

thanks for giving me solution to my problem triple- x.......

but my problem is how can i load data in 4x674595's from 7 pins of 16f505
1-clk 2.latch 3 RB2 is connected to sdata of frist 74595

4. Rc0 is connected to sdata of second 74595

4. Rc1 is connected to sdata of third 74595
4. Rc2 is connected to sdata of fourth 74595

sorry.............. for troubling u triple-x .i hope u send solution.......

[Guest]

[quote="chandrika"]Hi friends,

thanks for giving me solution to my problem

but my problem is how can i load data in 4x674595's from 7 pins of 16f505
1-clk 2.latch 3 RB2 is connected to sdata of frist 74595

4. Rc0 is connected to sdata of second 74595

4. Rc1 is connected to sdata of third 74595
4. Rc2 is connected to sdata of fourth 74595

sorry.............. for troubling u friends .i hope u send solution.......

[chandrika]

[quote="Anonymous"]

[dyeatman]

You are not trying very hard to find the info on this. The chips are wired in series.

Googling on "74595" returned numerous good hits. The second link it found had what you need.

See the following diagram.

www.tayloredge.com/reference/Circuits/74595.pdf

[chandrika]

no my chips(74595) are connected in parallel but these r conneccted to the 16f505 IC.each 74595 datapin(14)is connectd to pic 16f505 I/O pins .how to send data to 4x74595

[dyeatman]

You will have a BIG problem making this work at all.

The clk and latch signals going to all chips will cause the chip not getting data to clock all "0"s in during a load cycle... You need to be moving the C/S (LCLK) not the data line to each chip for this to work using the CCS driver.

It can be done but it will be complicated and you will NOT be able to use the CCS driver for this. You will have to write your own.

Why is it done this way? Is it a school project?

[chandrika]

thanks for ur suggestion thank u so much......

[triple_x]

hi,
dyeatman is right. Chandrika, u must get your hands dirty though, I mean must experiment the device from info u have, from there u can have the understanding, then u can expand as u wish.

As for 74595, test single chip first before proceeding to 4. Once u understand how the chip is working, implementing the others I believe will be easy.

Most of the guys here won't be doing others homework, but they are willing to give u help where possible. I'm also learning from the experts here...

[[email protected]]

void write_expanded_outputs(BYTE* eo) {
BYTE i;
BYTE j;
BYTE tmp; // ++added, to hold data passed by pointer

// ++reason: if u manipulate data passed by pointer, ORIGINAL data will also be changed!

// re-assign data to temp variable
// tmp = *eo;

output_low(EXP_OUT_CLOCK);
output_low(EXP_OUT_ENABLE);
for(j=1;j<=NUMBER_OF_74595;++j) { //
tmp = *(eo+j-1);
for(i=1;i<=8;++i) { // Clock out bits from the eo array
//if((*(eo+(NUMBER_OF_74595-1))&0x80)==0) // ++commented
if ((tmp & 0x80) == 0) // ++manipulate temp data
output_low(EXP_OUT_DO);
else
output_high(EXP_OUT_DO);
//shift_left(eo,NUMBER_OF_74595,0); // ++ commented
tmp <<= 1; // ++manipulate temp data, shift 1 bit to the left
output_high(EXP_OUT_CLOCK);
output_low(EXP_OUT_CLOCK);
}
}
output_high(EXP_OUT_ENABLE);
}