Why must set MCLR to 5v???

[babboy12345]

Why i dint connect the MCLR, n the LED like more nice than connect the MCLR to 5v?any comment??

 

[blueroomelectronics]

Huh? I'm not sure I understand you.

MLCR is RUN when 5V and RESET when GND

What does a LED have to do with it?

 

[be80be]

I bet he hooked a led to mlcr and 5volts vdd it lights up and looks good better have resistor there with that led. That's it maybe ??

 

[babboy12345]

1st, i feed a music to my RA0 as ADC input, then i just ADC the input and display all to my PORTB. When i got connect the MCLR to 5V, the LED look all turn on.If i dint not connect MCLR, the LED from RB0_RB7 will follow the music amplitude to light on.If amplitude high,led turn all on,if low.....

 

[tresca]

To answer your title question, MCLR is a pin that resets the PIC. Its not an input/output pin. By applying 5V to it, you ensure that your code runs from start to end. If its connected to gnd, then your code does not run, at all. It resets the address to the very beginning and just sits there. If you leave it unconnected (ie. floating), you can get something called floating ground. Basically, sometimes the code will run, and sometimes it wont.

 

[babboy12345]

for this, can i say that the total project is run at correctly?

 

[blueroomelectronics]

I have a hard time understanding what you're trying to say. Normally a 10K resistor from MCLR to VDD will do the trick. You can then use a pushbutton to ground to reset the MCU.

 

[babboy12345]

if i no puttting anythings to MCLR,is that my project still work??

 

[tresca]

if you dont put anything to MCLR, it MAY or not MAY NOT work. It will be completely UNRELIABLE. To make sure it WORKS, make sure that 5V is applied to MCLR by way of pullup resistor (as blueroomelectronics stated)

 

[babboy12345]

but how to solve my problems? If i wan get nice light,i need neglect the MCLR

 

[tresca]

Connect a 10K resistor from VDD to MCLR. Thats it.

 

[blueroomelectronics]

MCLR is an input only pin, has nothing to do with LED brightness.

 

[babboy12345]

not the bridness change,is the pattern change....

 

[blueroomelectronics]

Just tie the pin to VDD via a 10K resistor. Easy.

Post your schematic.

 

[babboy12345]

thx to u all.I noe wat u all say, plugging a 10k from MCLR to 5v.The problem is,when i do like this,i lose a nice pattern.If i do the correct way,i need to set the pattern again,but i have no ideal on it.............T_T

 

[blueroomelectronics]

The pattern is done by your program running inside the PIC. You have to change the software.

 

[Triode]

if you dont put anything to MCLR, it MAY or not MAY NOT work.

this is one of the things that confused me greatly when I first started with PICs about a month ago. I'd set up a basic led blinker and it seemed to switch on or off when i put my fingers near it. I didn't know to connect MCLR to anything, so it was up to the subtle energy fields surrounding the device, for a while i was confounded by its seemingly hand-detecting operation.

btw, im just a beginner, but coulden't he just turn off MCLR in code and not worry about it? thats what i usually do.

 

[blueroomelectronics]

If MCLR is off and your programmer does not support VPP before VDD you may never be able to reprogram it.

 

[homemade24]

10k pull up and then _MCLRE_OFF

 

[Triode]

If MCLR is off and your programmer does not support VPP before VDD you may never be able to reprogram it.

how would that happen? I know I've cut the power to my chips while they were running and didn't have this issue.