Arm Mbed and Pelion Device Management support forum

MAX32620FTHR 1-wire

Are there any examples for using the 1-wire port on these boards?
The arragement of the OWM_IO (P4_0) with the external pull up mosfett controlled from OWM_PUPEN (P4_1) has me stumped.
I can get the OWM running, but the line is never pulled to 0v, the best I can get is 2.2v
Even in direct GPIO control of the pins I’m unable to ever pull the output to 0v.

I’ve searched and searched, but found no examples of 1-wire being used on this board. So any help is greatly received.


How about this:

There’s a project here with some info too;

Thanks for this, I had seen this but unfortunately it’s for a different board with a slightly different mosfet arrangement.
Here is the output on my scope during a reset signal (should be about 500uS of 0v):

Here is the arrangement on the MAX32620FTHR
P4.0 is the one wire master, and P4.1 is the external pull up control.

I’ve think that P4.1 should be in open drain mode to pull the gate input to ground, but have tried every GPIO option avaliable in the book.

Yes, your reset pulse is not going very low.
I’m not sure whats the significance of the 1-wire pin here other than Q2 may be used to increase the parasitic power requirements if you don’t have Vcc to the sensor.

That R6 resistor will be problematic if it is actually 10ohms rather that 1-10k ohms.
Could be a design error.
If you can’t drive Q2 off from P4.1 then just choose another I/O pin, I have used DS1820 1-wire sensors on both the 32620 and 32630 boards using a 4k7 ohm pull up to Vcc.


I’ve just checked my board, R6 is 10 ohms.
I will be changing mine to 4k7.

R6 is not at fault here, it’s Q2.
Maxim have drawn a P-Channel mosfet, but PMZ600UNE is a N-Channel.
The other dev boards in the range (MAX32625PICO, MAX32630FTHR) have a similar layout but with a P-Channel.

Paul - When you say you’ve used 1 wire on both 32620 and 32630 boards, do you mean on this exact development board (MAX32620FTHR) using the MCU One Wire Master on P4.0?

Because of this board errata I’ve ended up bit-banging One Wire using a GPIO for this project.

I tend to use this most of the time, but depends if you are using a different 1-wire device:
Haven’t tried the Maxim’s version, I would but because there are several other issues with Maxim’s libraries on Mbed mainly with serial UART interrupt and speed issues I gave up and they’ve been in the cupboard since.
Personally I would remove Q2 if its incorrect, that could cause other issues loading that I/O pin.