My Laptop is not detecting my Tiva C Series TM4C123G LaunchPad anymore.

Hello Rupayan,

Is the LaunchPad not even showing up as a Unknown Device? what were you doing last with the LP when the issue occurred?

Regards
Amit

Thanks for the reply Amit,

I was working on a project which worked fine the previous night.But on the next morning when switched on the device(which did't powered on) i noticed that positive wire of the battery came out of the breadboard hole that was connecting it to the input of 9v to 3.3v voltage regulator and tried to insert it back , the power came back and the message on Nokia 5110 LCD(connected to the LP) appeared but only for few seconds and since then this problem is occurring.

Hello Rupayam,

Could be a damage to the device (when a live supply) got connected. Check the output of the LDO to see if there is still 3.3V?

Regards
Amit

Hello Amit,

Sorry,Can you tell me what is LDO in Launchpad

Regards,
Rupayan

That's a, "Low Drop-Out Regulator" - which provides the 3V3 required by your MCU (& possibly other) components. 

But - 9V into such a regulator may be too much - you must check the Regulator's specification.  The exact part no. for that regulator should be included w/the LPad's schematic & bom.

From what you describe - it seems that the voltage regulator has been damaged. Most such regulators will accept 5V (standard USB provision) and should run properly w/that as input.   As Amit noted - you must carefully probe your board for 3V3.   (I'd do that not on a fine-pitch part - but instead at a header pin - which is included on your board.

That said - there is a "best of all" scenario for you - 9V batteries are the least efficient, most costly and low on output power.   You may well have sufficiently discharged that battery - and w/out adequate input voltage - your MCU will never "see" the JTAG calling...

Hello Rupayan

The LDO is the component U8 on the board. Please refer to the schematics of the TM4C123 Launchpad to see where the probe on the output voltage can be done.

Regards
Amit

Hello Amit,

Sorry for the late response,I was not talking about the regulator on the LP but the discrete regulator(LM 1086) I bought seperately to convert 9v to 3.3v.I developed my project by taking power from my laptop via USB cable of the LP.Only after comepleting and testing my project i decided to power it from a 9v clip on battery and after converting it to 3.3v via regulator I powered the LP and everything worked as before but on the next day when i powered my LP with battery again it didn't powered on,i noticed that the positive(red) wire came out of the breadboard hole and i reinserted it and LP switched on and message on the 5110 Nokia LCD display came up but only for short period of time.Since then my Laptop is not detecting the LP(even though green power indicator  LED was on ) and also all the peripherals connected to the LP(via the port pins) are not receiving any data from it.

Rupayan Das said:

even though green power indicator  LED was on

That may not prove sufficiently convincing.   That Led will illuminate at voltages below 3V3 - while the MCU will not perform to specification @ "out of spec" input voltages.  

Our firm has long employed, "Windowed Comparators" as far more effective, "Power Monitors."  These will illuminate one or several Leds "only" when the voltage to be measured is within "both" an upper & lower limit.   This is not the case w/the power monitor on (most) inexpensive such boards - which will continue to light even when the supplied voltage is "outside" of spec!   (i.e. many/most red or green Leds will light @ Vin of 2V2 (or less!))

*** Of greater importance - you made a rather large error in converting to 3V3!   Introduced to your board - that's in CONFLICT with the "normal" 3V3 regulator - resident upon your board!   I'd bet that's the "real source" of your issue!   Such cannot be "good" for the resident 3V3 regulator on your board!  

If you must use an external supply - convert instead to 5V - and feed that 5V to the board circuit/component normally receiving 5V from the USB connector.

I do not recommend feeding your board w/3V3 - even if you can "isolate" the original regulator's output.   Other circuit elements "may expect" 5V - and if left floating - the overall behavior may be suspect...

Hello Amit,

But also the LP is not talking to the connected peripherals even after I powered the LP through my Laptop. It seems that port pins are also damaged.
What is your guess on what kind of damage it may cause to the LP if you power it via an external 3.3 voltage regulator?
What is your advice on how to power this device via an 9v battery?

Hello Rupayan,

Heed cb1's comments as they have value above thought. As for any possible device damage, check on the VDDC pin for 1.2V. If it is not 1.2V then perhaps some power pin got damaged

Regards
Amit

Pardon - but your questions are (anticipated) and (answered) w/in my 08:30 post, earlier this day...

Sorry cb1, my mistake, I wrongly read the post written by you as written by Amit,thank you very much for the advice.
Vddc pin is 1.2v.What is the interpretation of this?

Regards,
Rupayan

Hello Rupayan,

So the core supply is up and working. So voltages are fine from debug perspective. Check if RST_n pin is high and then try to run an unlock sequence. Other than that I can't think of anything else that may be blocking.

Regards
Amit

As Amit noted prior to your (most recent) post - the MCU core should be at/around 1V2.

That said - the output of the LPad's 3V3 regulator remains suspect.   Have you measured 3V3 - at the board's header pin (for safety) as I (several posts back) suggested?   With the conditions you describe I have concern over the health of that (on board) 3V3 regulator.

Further - I'd cease all use of your 9V to 3V3 power input - and return to USB cable power input, only.   One further horror - your improper injection of 3V3 may have damaged some of that USB-5V input circuitry - as well.

It's critical that you:

a) cease use of the 9V to 3V3 (home-built) converter as a power input.    (w/out proper regulator filtering the output may "sing."

b) measure the 3V3 on the marked, board header pin - when the board is only, (properly) powered - from a USB cable.   (as intended)

c) report the result of that measurement

Any attempt to "clear and/or restore" your MCU is doomed if your board does not have proper/stable 3V3!

Hello cb1,

The LDO output is at 3.3v , +3.3v pin is at 3.3v and the vddc is at 1.2v and RST_n pin is at 3.3v. 

How to do the unlock sequence as suggested by Amit ?

Rupayan Das said:

The LDO output is at 3.3v , +3.3v pin is at 3.3v and the vddc is at 1.2v and RST_n pin is at 3.3v. 

Much of that is, "Good News" yet is the LDO you mention the "original, on board V Regulator?"

Have you reverted to powering your board "ONLY" from a USB cable?   If you continue to inject "foreign" 3V3 you will have "contention" between on-board & foreign output regulators - never good!

I believe that "LM Flash Programmer" includes the unlocking sequence - yet it's been (5) years since we used that.   There are many posts on this forum - perhaps even Amit's "Diagnosing" (atop the forum) details the how, where, when to "unlock."

Again - 9V batteries are among (if not the worst) batteries in terms of cost & power output.   And you should avoid injecting 3V3 and inject 5V via the USB connector - even (and especially) if you persist in using non PC/USB as the power source.     You should be able to find many, "rechargeable, battery based" (not 9V) 5V output Power Packs (output via USB style connectors) ideal for powering your LPad!

Hello cb1,

I have downloaded the LM Flash programmer and tried to unlock the LP by following the steps posted atop the forum by Amit.

1. I first removed power by pulling out the USB cable.
2.Pressed the Reset button.
3.Ran the unlock sequence by the "dialog box" by clicking on the "unlock" button in LM flash programmer.
Then an information message came stating that-"assert and hold the Reset button while powering up the device"(not released reset button yet).
4. Powered the LP by reconnecting the USB cable to the Laptop.(Reset button is still in pressed condition)
5.while still pressing the reset button I clicked on the "Ok" button of information message, immediately an error message pops stating that-"**ERROR**:Failed to unlock the connected device!"

Can you guess what the problem is?

Regards,
Rupayan

Sorry - this is very "Vendor specific" so we'll need Amit or another here w/recent, focused, Unlock experience.

You suggest - but do not state directly - that power is now being (properly) supplied from the PC via a USB cable.   Is that correct?

While attempting this "unlock" you should have removed any/all interconnected cables, devices - anything which may interfere w/the process.

Your last post is most excellent, detailed, properly sequenced - very much (I believe) moving in the right direction.

I remain fearful that your on-board 3V3 (LDO) regulator may have suffered during the injection of a competing 3V3 supply.   Unknown is how you measure that 3V3?   Scope would be best - sometimes when regulators like yours are damaged they "sing" (oscillate) and the peaks/valleys are outside MCU specs.   It also is critical that you carefully monitor that 3V3 level during the times you are interacting w/LMFlash - especially during the "unlock."   One last point dawns - have you correctly identified your MCU when LMFlash requires a, "Class Choice?"   (again I'm no help in that area - yet a mistake there will spoil your unlock attempt.)

Hello Rupayan,

The Reset button must be pressed when you plug the cable back till the message does not come "Release reset". Also note that it the USB cable on the debug MCU side that must be used to power the device.

Regards
Amit

Hi Amit,
I suspect that this poster is not the "first" - nor will he be the last - to inject 3V3 into his LPad w/out first "disabling" the on-board VReg. By my read, 5V is so much safer - proves a "less destructive" choice. And again - there are hundreds of USB chargers - which often prove suitable for powering the LPad via a normal USB cable - yet "free" from any PC...

Hello cb1

Mystery surrounds the use of 9V to 3.3V

Regards
Amit

Amit Ashara said:

Mystery surrounds the use of 9V to 3.3V   

I'd suspect that poster sought, "freedom" from the PC.   (even a laptop)

Boards - LPad sized/priced - may prove more attractive in "messy/hostile" environments - free from their PC tether...

9V to 5V0 would have prevented this misery...   (perhaps a caution should attach to LPad writings...)

Hello cb1,

Yes,I have powered the LP using the  USB cable on the debug side of the MCU from my Laptop.The LP was free from all the peripherals attached to it while performing unlock sequence.

You are correct cb1,my intention was to free my LP from the Laptop.In attempt to do this I attached the negative side of the 9v clip on Battery to the GND pin and output of LM 1086(9v to 3.3v voltage regulator) which was 3.3v to the +3.3v pin of the LP. Also the negative side of the battery was the system ground for the entire project.

Regards,

Rupayan

My friend - you are so clear & detailed in your writings - if (only) you had "Posted here" first - asking about your proposed (new) voltage input!   (lesson learned - by/for yourself & others - one hopes)

The fact that your board still (appears) to produce 3V3 is heartening - although unclear is the method of measure.   Scope may detect "hills/valleys/oscillation" - DVM not so much.  

Might you be able to purchase or borrow a 2nd LPad?    Then connect just as you do now - and determine if that (2nd) board works?   I won't have time to properly review the LPad schematic - but can recall other clients who - during power-supply "collision/contention" developed issues w/in the earlier (i.e. the 5V) power stage.  (delightful that)

Amit's post provided very exact "unlocking" details.    Might you attempt that again - precisely following his detailed instruction?    (i.e. change nothing!)

If you could place your DVM in current measure mode - measure the board's current - and report - such may prove useful.

We've not been told if you have access to a scope and have monitored the board's 3V3 during the critial "unlock" procedure.   (where I expect current draw to be highest)