Electronics > Microcontrollers

Poweron problems using PIC and automotive application

<< < (3/4) > >>


--- Quote from: mtechmatt on July 10, 2012, 04:11:02 pm ---
--- Quote from: deephaven on July 10, 2012, 03:38:37 pm ---PICs don't normally need a capacitor on their MCLR pin as they have a built-in reset timer. I would ditch the capacitor and both diodes, just have a 10K pull up resistor and the programming pin connected straight to MCLR.

--- End quote ---

Could this cause issues with the 13v being back fed into the circuit when programming?

--- End quote ---

If you are using MCLR for I/O as well, then yes it could cause possible issues with what else you've attached to it. In that case you would need the diodes.


No there is no other usage of the MCLR line other than for programming.

I have found loads of ICs to do this job on the reset pin for me which will probably simplify things greatly, is the PIC active low(I think it is as I tie to VCC) rather than active high?

I am confused to which way round the active goes. The PIC needs 5v on the MCLR line to be 'running'... can someone please clarify?

Would this be a suitable device, it appers to put out 5v once the trip of 4.65v has been reached..


after looking at the datasheet, it appears that microchip recommend this device (MCP100) using an active ow, to drive their standard MCLR (which has a line above, meaning inverted, or reset is NOT active when low.)

If I am wrong can someone point it out please.... Cheers

All very confusing!! :)

Short Circuit:
Reset is active when MCLR is low, the PIC is active when reset is not active, so when MCLR is not low. :)
If the MCLR from the PIC is also an output (many CPU reset pins work bidirectional), then you'd want a
reset device with OpenCollector/OpenDrain output and use the external pullup resistor.


So, I know the PIC is active when MCLR=5v (high)
so if my MCP100 is an ACTIVE HIGH type, does this mean its output is HIGH when it is finished, or only HIGH, when its RESET feature is active. Obviously I want the one that outputs 0v when the power first comes on, and after it reaches its threshold, it needs to go HIGH. I think it is the MCP100T as I have chosen in that datasheet, though I really dont want to get it round the wrong way at this point :)



[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Go to full version