EK-TM4C123GXL has SPI signal too low

Hello Duy-Ky

Which SSI Instance and pins?
I believe the problem is with 0Ohm resistor (similar issue reported a few weeks back) which is between PD0-PB6 and PD1-PB7, if the slave is also using the pins PB6 and PB7 while SSI is being used on PD0 and PD1.

Regards
Amit

Hi Amit,
I'm using SSI0 and external slave SPI, not internal one in TM4C123 as in the example
Thanks,
~Duy-Ky

Hi CB1,

TM4C1223 has 4 SSI's and SSI2 has its pins TX & RX tied to CLK & FSS of SSI3. That's why I'm using SSI0 has no pins shared with others when seraching those pins on the schematic of the PDF file!

I guess these pins has high output impedance so it cut half the voltage in interfacing with other?!?!

Thanks, CB1

~Duy-Ky

Duy-Ky Nguyen88210 said:

I'm able to get SPI (SSI in TI term) signal on pin header on the EK-TM4c123GXL.

 Please specify which pin are you using, from SSI0 I suppose Port A, are you sure there where no interference with mentioned resistor?

Duy-Ky Nguyen88210 said:

However it signal is ONLY HALF of specs (1.5v vs 3.3v) when connected to SPI slave. The level is 3.3v when no connection.

 This can leave me suspect of wrong connection, is the pin output connected to input of slave?

 Which kind of slave are you connecting to?

Duy-Ky Nguyen88210 said:

I have a EK-LM3S2965 and checked the level is the same 3.3v when connected to the slave

 This enforce suspect of wrong connection, did you checked old-new pin equivalence?

Duy-Ky Nguyen88210 said:

I tried with max strength 8MA only to add 0.2v to get 1.7v

 Again resemble a contention between two output, is the external pin driving low? try a LED just to see if output can drive few mAmps to ground and also if external pin is open or not.

Duy-Ky Nguyen88210 said:

What's else I can do ?

 Document more about what happen, measure current between ssi pin and external slave is a good idea, just led and resistor can do the job.

Hello Duy-Ky,

I checked the SSI0 pins on a scope with a slave connected and never does any of the pins come to 1.5V. Either it is 3.3V or 0V. Cam you check the pin connectivity (most probably a TX pin is connected to the Slave TX pin)

Regards
Amit

Hi Amit,
As mentioned in my previous email, the signal level is 3.3v with no external slave SPI connection, but 1.5v if connected.
So, you see 3.3v WITH or WITHOUT a load ? Needless to say that the EK-LM3S2965 I have, it behaves the same with or without load.
Thanks,
~Duy-Ky

Hello Duy-Ky

As mentioned in my last post as well: Can you check the pin connectivity. It seems to me (and to roberto) there may be a contention if two output pins are connected.

Also is the 1.5V on all the pins or only one pin. Can you please specify which pin(s) are affected by the same, are you using a scope to check the same and what slave device is this (part number)

Regards
Amit

Duy-Ky Nguyen88210 said:

As mentioned in my previous post, signal level is 3V3 with no external SPI connection, but 1V5 when connected.

Duy-Ky - there's a difference between, "as mentioned" and, "clearly explained!"  Three experienced guys "missed" your "mention!"  (such may indicate lack of clarity...)  Your use of, "signal level" (singular) suggests that just ONE SPI signal has shrunken - is this the case?  And - if so - which one?

How are you powering your external SPI slave board?  Is it powered - both up & down - via the same 3V3 which supplies your MCU board?  If so - have you measured that 3V3 (recently) - both @ MCU board & at slave SPI board?  And - have you a duplicate slave board - or slave SPI device?  (forcing your forum "helpers" to troubleshoot some derelict, ebay sourced part - is not an especially good use of resource...)

Hi,
Everything is correct, but the power line to the slave SPI was broken!!!
I've been using the same SPI slave, it is SPI Touch-Screen LCD, to find best fit for it, starting from ATMega Arduino, to BeagleBone, then LM3S2965 and now TM4C123. That's why it cannot be wrong on the LCD side as each board has its own set of 6-pin color ribbon cable. For some reason, the power pin has bad contact for this board!?!?
Now it's up full voltage 3.3v.
I'm so sorry for the "noisy inconvenience" it may cause to you, guys.
Your help is greatly appreciated.
So sorryyyyyyyyyyyyyyyyyy
Thanks so much,
~Duy-Ky

cb1_mobile said:

How are you powering your external SPI slave board?  Is it powered - both up & down - via the same 3V3 which supplies your MCU board?

Does this "remote diagnosis" pound your failed SPI "nail" - solidly on it's head?

If ever a post deserved, Verified Answer...

Hello Duy-Ky

That is fine. I believer cb1 and Roberto do achieve a verified answer that could be used to trouble shoot such scenarios.

Regards
Amit

Yes, there's no power to the slave SPI device to pull down thew voltage level

cb1_mobile said:

cb1_mobile

How are you powering your external SPI slave board?  Is it powered - both up & down - via the same 3V3 which supplies your MCU board?

Does this "remote diagnosis" pound your failed SPI "nail" - solidly on it's head?

If ever a post deserved, Verified Answer...

There is NO Justice!

The TFT LCD consumes about 500 mA by itself. It's unwise to get the high current from the board. So it has its own power supply separated from the board

Here is the true justice.
1) I found the problem before reading reply regarding power supply
2) I confirmed the power problem I found consistent with the content in the reply
I tried and failed to confirmed earlier as I had several error in clicking on "reply" button

What else should I do ?

What else you're looking for ?

I post my problem to the forum, it does NOT mean I stop working to solve my problem.
It just means I don't have to spend time to solve the problem already solved by someone else. It's a waste to "reinvent the wheel". I just want save my time to work on other issues. More than 50% I solved the problem by myself after I posted on the forum.
I just had a solution to my CCS problem before I could solve it. So I just click "Verify Answer" with a BIG THANK.
The only persons who might really work to solve the problem are TI employees. I doubt if community members really works to solve the problem, unless for their own interest.

I see the forum is where to SHARE EXPERIENCE first, not where to score the point first.

I save that time to

Duy-Ky Nguyen88210 said:

What else you're looking for ?

Simple forum justice - that is all.

Mine was the first post to urge you to check the power to your SPI module - TFT has no bearing on this.

You "verified" another's post - (thus you knew how to do that - verify should be a check box - not on your post but on each of your "helper's" responses)

You really should verify the original "answer" (no power @ SPI Slave) as well as award to another...