Port A not 5Volt tolerant, crosstalk between PA1 and PA2?

andywild · ‎2008-01-18

Posted on January 19, 2008 at 06:51

andywild · ‎2011-05-17

Posted on May 17, 2011 at 12:21

Hi all,

an EXT1-Int is configured for PA1 and it works fine.

At PA2 is a 5Volt signal. If PA2 makes edges from 5V to 0Volt, then an EXT1-Int is generated! (regardless what edge is configured for EXT1-Int)

If I lower the voltage of PA2 below 4.8 Volt everything works fine!

This looks like crosstalk between lines which are close together!

And this reminds me to a 5V tolerant problem with the uPSD3300 series:

If on a port which is 5Volt tolerant according to data sheet has digital and analog lines close together, then the analog inputs are affected by the 5V transitions! This problem was never fixed in the uPSD3300 series.

Are we going to have similar problems with STM32?

Thanks

Andy

16-32micros · ‎2011-05-17

Posted on May 17, 2011 at 12:21

Dear Andy,

Are you sure that you have good pcb design not affecting this behavior. Could you please share us with your PCB design files and Schematics and some scrennshots to investigate more about your case ? and provide as well the chip data code you are using ? thx, STone-32.

andywild · ‎2011-05-17

Posted on May 17, 2011 at 12:21

Hi STOne32,

I am using the MCBSTM32 Board from Keil.

Actually I have tested the same configuration also with PA8 and PA11. Here everything works fine, because PA8 and PA11 are not close together.

But then I tried the following: PA12 is configured as EXT-Int. I put a 5Volt to 0Volt transition on PA11 and: Bingo! PA12 Ext-Int is triggered! (I know Ext-Int 10-15 are combined to one Handler, so EXT11-Int was definitely not enabled!)

All the effects can be stopped if you gradually reduce the power of the 5Volt signals below approximately 4.8Volts. Then everything is ok.

Hope that helps you

Andy

16-32micros · ‎2011-05-17

Posted on May 17, 2011 at 12:21

Hi Andy,

I'm stucked last time :-Y to not see that is Normal, In fact PA2 is not a 5Volts tolerant but only standard ( 3.6 max) capable, you can refer to datasheet in the Pin definition table only I/O marked with FT are 5volts tolerant, So it is forbidden to apply a voltage greater than 3.6 at PA2 and it is risky ( out of product Specification),have a look at Absolute maximum rating :o too. That is all the story

STOne-32.

[ This message was edited by: STOne-32 on 18-01-2008 19:01 ]

andywild · ‎2011-05-17

Posted on May 17, 2011 at 12:21

HI STOne32,

thank you, this is a very good hint!

But I could provoke the fault also with the lines PA10/PA11 which are 5Volt tolerant....

But at the same time I had the 5V signals also connected to PA1/PA2 which is not allowed. Maybe this PA1/PA2 5 Volts affectes other part of PortA also.

So I will rewire to only 5Volt tolerant pins, and then I will recheck.

Thank you very much for your help, I just didnÂ´t expect only a part of a Port is 5V tolerant!

Andi

andywild · ‎2011-05-17

Posted on May 17, 2011 at 12:21

Dear STOne32,

I reconnected my four 5 Volt lines to 5V tolerant lines and there is no crosstalk anymore. Everything is ok. IÂ´m glad that I didnÂ´t destroy the CPU while connecting 5Volt to PA1!

Thanks again for your help

Andi

PS: Some days ago I asked for the purpose of SysTick Calibration register.

The SysTick rate is only dependant on the Load Register, so what is the CALIBRATION Register used for? Where can I see the 1ms rate calibrated by this register?