topic Re: What kind of reset is triggered by the POR_B pin? in i.MX RT Crossover MCUs

What kind of reset is triggered by the POR_B pin?

mastupristi — Tue, 11 Jun 2019 08:02:53 GMT

I'm referring to RT1051.

on the Reference Manual (page 1242/1243):

So the Cold reset does not reset all the peripherals, unlike the POR reset.

The name of the POR (PowerOn Reset) reset makes me think that it can only be triggered when the micro is powered. Is that right?

What happens if I assert the POR_B signal (is pulled down) when the power supplies are already on and stable?

On the Datasheet I found (page 16):

Does the POR_B signal cause a cold reset or a POR reset?

best regards

Max

Re: What kind of reset is triggered by the POR_B pin?

kerryzhou — Wed, 12 Jun 2019 06:07:51 GMT

Hi Massimiliano Cialdi,

Please check these information from the reference manual:

the POR_B is used to reset the entire chip including test logic and JTAG modules.

Then you can consider the POR_B as the POR reset.

Actually, the MIMXRT1050-EVKB board also use the reset button connect to the POR_b, I have test the code, when debug, if press the reset button, the debugger will be disconnect, so you can consider it as POR.

Wish it helps you!
Have a great day,
Kerry

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Re: What kind of reset is triggered by the POR_B pin?

mastupristi — Wed, 12 Jun 2019 07:45:39 GMT

Kerry Zhou wrote:
Actually, the MIMXRT1050-EVKB board also use the reset button connect to the POR_b, I have test the code, when debug, if press the reset button, the debugger will be disconnect, so you can consider it as POR.

This is not correct. It looks like you've never seen the EVKB schematics. Have you ever really worked on it or do you speak by hearsay?

On the EVKB the POR_BUTTON is NOT directly connected to POR_B pin:

the POR_BUTTON it is connected to pin MR of the power supply monitor U5, which in turn removes the enable to the DCDC converter U3. So the DCDC_3V3 is turned off.

When the DCDC_3V3 is turned off, the U2 power monitor asserts a reset that it is connected directly to the POR_B pin of the microcontroller.

The POR_B pin of the micro is then connected to the JTAG J21 connectors and to the J25 connector.

So if you tried by pressing the POR_BUTTON SW3 button, you caused a power failure, and then a powerup sequence as described in the reference manual. In this case it can be explained so that the JTAG disconnects. In summary, it is true that pressing POR_BUTTON causes the assertion of the POR_B signal on the micro, but as an indirect consequence of the power supply drop DCDC_3V3.

The case I would like to clarify is to drive low the POR_B pin without turning off the DCDC_3V3 power supply.

I encourage you to try using the signal from the J25 connector (obviously closing the J26 jumper). Does the JTAG disconnect in this case or not?

best regards

Max

Re: What kind of reset is triggered by the POR_B pin?

kerryzhou — Wed, 12 Jun 2019 09:52:26 GMT

Hi Max,

Thanks a lot for your detail reply.

Yes, I have tested the J26_1, and connect it to GND, this is the result:

You can find the debugger is stopped after the POR_b connect to GND.

If you still have any question about it, please kindly let me know.

Have a great day,
Kerry

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