SPI Questions & Debugging

aggiehorns

Other Parts Discussed in Thread: CC3200

I'm debugging some SPI issues and observing some behavior that seems strange to me. Several questions.

1) What voltage levels should I be seeing on the GPIO ports? Running the "sdhost" sample project, when the routine MAP_PinConfigSet(PIN_08,PIN_STRENGTH_4MA, PIN_TYPE_STD_PU) executed PIN_08 is pulled high. On the multimeter I am reading 0.8V, not 3.3 which is what I would have expected. Is 0.8V a correct voltage level?

2) Here is a comparison of waveforms that I see (D0=CLK, D1=MOSI, D2=MISO) with and without external pullup resistors added to MISO and MOSI.

WITH EXTERNAL PULLUP ADDED

WITHOUT EXTERNAL PULLUP (INTERNAL ONLY)

Without external pullup resistors on MISO and MOSI the CLK only has three pulses. This to me is very strange. The CLK should be pulsing regardless of whether the logic levels on MISO and MOSI are sufficiently high, right? Note the captures from above are from executing SendCmd(CMD_GO_IDLE_STATE, 0) in CardInit() in main.c

over 8 years ago

0 aggiehorns over 8 years ago

Prodigy 215 points

Note the captures from above are from executing SendCmd(CMD_GO_IDLE_STATE, 0) in CardInit() in main.c

0 made4engineering over 8 years ago in reply to aggiehorns

TI__Mastermind 27360 points

Hi there,

I suggest there may be something wrong with the way you are measuring the voltage levels. 0.8 V is not something you should get from a digital pin of the device without using external pull. I don't think that state of the software is the same from one waveform to another, since pulls should not directly affect this behavior.

Regards,
Aaron

0 aggiehorns over 8 years ago in reply to made4engineering

Prodigy 215 points

How might I be measuring things incorrectly? Multimeter from GND to the IO pin...

When I use the SD Host peripheral, and pull pins high, I get 800mV. If I use the SPI peripheral instead, I get 3.3V.

0 made4engineering over 8 years ago in reply to aggiehorns

TI__Mastermind 27360 points

Hi there,

You should be using an oscilloscope for reading the voltage levels of the waveforms. Can you take a look at these to make sure? Also, does the SD host example in the SDK give you the same results?

-Aaron

0 aggiehorns over 8 years ago in reply to made4engineering

Prodigy 215 points

> You should be using an oscilloscope for reading the voltage levels of the waveforms.

You did see the screen shots I posted, right? Those are from an oscilloscope. When a pin is pulled high though, and set to high, you can probe it with a multimeter.

> Also, does the SD host example in the SDK give you the same results?

This is the SD host example... ? You mean sdhost vs sdhost_fatfs? Yes, both give same results. However, the SPI example works and I do not experience this behavior when using SPI peripheral instead of SDHOST peripheral.

0 made4engineering over 8 years ago in reply to aggiehorns

TI__Mastermind 27360 points

HI,

What sort of board are you using to run these tests?

-Aaron

0 aggiehorns over 8 years ago in reply to made4engineering

Prodigy 215 points

I'm not sure what you're asking. I'm using a standard CC3200 Launchpad. My measurements are with Agilent/Keysight benchtop scopes.

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