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# 1   2008-05-27 20:53:23 Working with I2C2 on ST Primer

armaniake
Member
From: USA, Texas
Registered: 2007-08-22
Posts: 38

Working with I2C2 on ST Primer

Hi,

I have been able to run the I2C2 bus. But while testing my solution, I can see a strange thing on SDA, SCL and also the power pin VCC3. I do not know how to attach a file but I have a scope screenshot showing that when I press the RUN button in debug mode, I can see burst of pulses with a primary frequency of 300Hz on the SDA, SCL and VCC3 lines. The burst are identical on each of the observed lines.

Those burst disappears when we leave debug mode but they also re-appear when the unit is running (not in debug mode). Also, just incase, I reflashed the Primer with OSCircle 1-7 to erase everything, I can still see those pulses.

Those pulses stops when I enter my application from the menu...

What are those pulses present on those 3 wries: SDA, SCL and VCC3?

Thanks for any ideas,

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# 2   2008-05-28 07:17:10 Working with I2C2 on ST Primer

Francis
Administrator
From: France-Grenoble
Registered: 2007-07-09
Posts: 890

Re: Working with I2C2 on ST Primer

Does it look like noise, or is it a real pulse?
Anyway, it is probably linked with some other signals. Some suggestions:
   1. The backlight white leds modulated with a PWM (highest current consumption).
   2. the LEDs
   3. The SPI (communication with the MEMS).

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# 3   2008-05-28 14:41:32 Working with I2C2 on ST Primer

armaniake
Member
From: USA, Texas
Registered: 2007-08-22
Posts: 38

Re: Working with I2C2 on ST Primer

Thanks for your ideas.

They are real square pulses, swinging from Vcc to 0V in  a clean and sharp way. It is like the VCC is pulsed, impacting then other signals.
The base frequency is about 300Hz (slightly moving back and forth), each burst is 781us long and the burst is made of what could looks like a PWM signal but I would not swear.

My App runs entirely in Application_Ini(). It is a very small app (a kind of hello world but printing something coming from I2C2 as a parameter). And I have seen that during my application being executed, the pulses are gone. But it starts right after I leave Application_Ini(). I have commented everything in Application_Handler(), but the pulses are still there...

I have tried to use LCD_SetBackLightOff() to shut down the backlight but it had no effect.The backlight stayed on. I used also LCD_SetBackLight (2000) to dim it but it dim anything (OS V1.7). Not sure what is the problem there. Note I'm running RKitARM Rev 1.03.0004 (I have not updated yet to your CD image Rev 1-4).

I have ran the primer from BATTERY, and it does the same. So, it is not coming from my USB.

Regarding the MEMS generating those pulses, it looks unlikely as the MEMS consumes not even 1mA.

For the LEDs, when the Primer is being programmed, the green LED flashes but I see no pulses on the platform VCC3. Pulses starts only when the Primer comes to life (in debug or non-debug mode).


Do you see that also on your platform? Am I the only one who saw that?



I'm puzzled, I have to say.

Regards,

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# 4   2008-05-28 15:16:37 Working with I2C2 on ST Primer

ar3000a
New member
Registered: 2008-05-27
Posts: 3

Re: Working with I2C2 on ST Primer

scope probe float from GND?

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# 5   2008-05-28 15:42:29 Working with I2C2 on ST Primer

armaniake
Member
From: USA, Texas
Registered: 2007-08-22
Posts: 38

Re: Working with I2C2 on ST Primer

I have to say, what you are suggesting makes a lot of sense. Unfortunately, all probes GND are connected to the primer. I tried with one GND, 2 and GND (I have 3 probes currently on the Primer).


Thanks for sharing your idea.

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# 6   2008-05-28 17:40:14 Working with I2C2 on ST Primer

armaniake
Member
From: USA, Texas
Registered: 2007-08-22
Posts: 38

Re: Working with I2C2 on ST Primer

Hi guys,

Thanks to ar3000a suggestion, I realized I was using the wrong pin for VCC. I was using as VCC J1 pin1, which is the SPI MEMS MOSI signal...

Thanks for your help.

Armand

P.S. As a side note, even though it was complete inattention from me, it would be nice to have a silkscreen mark on the PCB that indicates pin 1 of J1

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# 7   2008-05-28 21:09:34 Working with I2C2 on ST Primer

Francis
Administrator
From: France-Grenoble
Registered: 2007-07-09
Posts: 890

Re: Working with I2C2 on ST Primer

The next version of the Primer will have a soldered connector. No more mistake...

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