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Programming/debugging MSP430(G2553) while not common ground


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hi all there,

 

i would like to ask the forum how to programm or debug MSP430 (sbw) when the chip is powered from a supply which has other ground potential than the programmer/debugger. i've simply tried to join the grounds of a dev board (which gets the power from usb) and the chip but this it did not worked for me.

of course, if i do supply the chip from usb all works.

geting the chip out every time or turn all the other circuitry off is not possible (when debugging or TSSOP) so i wonder where the problem could be. should i make some pricey gadget like the bidirectional optocoupler, which would ignore the supplies? i've 47k resistor with reset.

thanks

al.

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i had the same setup as on p16 http://www.ti.com/lit/ug/slau318e/slau318e.pdf , except the cap to ground was 2.2nF. recently i get rid of the cap as i had problem to program the board (checked with oscilloscope and the signal edges seemed too much rounded) if the 2.2nF cap was in place.

 

i'll put the cap back, this time exact 1nF  and double check the grounds,  good to hear that this must work. will post the result.

 

mysetup.jpg

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The Launchpad G2 board is running at 3.6V, while your circuit is running at 3.3V. I don't think it should matter, but maybe it does...

Your programming cable must have these signals connected:

SBWTCK

SBWTDIO

GND

 

Since SBWTDIO is bidirectional, you can't use classic isolation circuits with it. I don't think SBWTCK is bidirectional, but I'm not sure.

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The Launchpad G2 board is running at 3.6V, while your circuit is running at 3.3V. I don't think it should matter, but maybe it does...

Your programming cable must have these signals connected:

SBWTCK

SBWTDIO

GND

 

Since SBWTDIO is bidirectional, you can't use classic isolation circuits with it. I don't think SBWTCK is bidirectional, but I'm not sure.

ADuM1250/1251 are dual I2C opto-isolators: 1250 is bi-directional on both SCL and SDA; 1251 is bi-directional only on SDA. Only other thing needed would be isolating any other inter-connections. Perhaps either would be useful?
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As a note, if you have the MSP-FET it will follow the voltage you are providing from the external supply if you connect the pins correctly (it has a pin for inputting to it an external voltage instead of having it provide a voltage to your board). It's not really good to have the debugger and supply at different levels and the communication may not be reliable.

 

Since SBWTDIO is bidirectional, you can't use classic isolation circuits with it. I don't think SBWTCK is bidirectional, but I'm not sure.

 

^^This is correct - SBWTDIO is the bidirectional one. There's way more details in www.ti.com/lit/pdf/slau320 - section 1.2.1.3 calls out SBWTDIO as being bi-directional vs SBWTCK which is controlled by the tool. Something you'll want to be careful with if you use isolators or something on these lines is the speed - I've seen people try to do this and had it not work before because their isolators screwed up the timing of the SBW too much. You probably want something that will be pretty responsive and not add much delay.

 

One other one I'll throw out there: there is also an isolated JTAG tool out there if you ever really need that (probably overkill for this though, but I know smartgrid guys that use this): https://www.olimex.com/Products/MSP430/JTAG/MSP430-JTAG-ISO-MK2/

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I do this all of the time with a board that is independently powered by a battery. In theory, joining the ground is all that you need to do HOWEVER it depends on the power source for your MSP430 and what IT is referenced to. Short of a very complicated explanation, if you connect the 3 pins that @@roadrunner84 suggested and plug the Launchpad into a laptop running from battery (not plugged into the wall) I think that you will be ok. If any type of high voltage is involved be very careful, this could be dangerous.

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SOLVED: as @@Lgbeno assured me that he is using this method and other of you also suggested that this should work I've reconnected all the wires and run the programmer - this time it was success from beginning (i was prepared to check each wire and and also check SBW with scope, so i consider the circuit was really scared of it).

 

floating ground of my transformer was joined with ground of the programmer (launchpad) powered from usb and 2 sbw were used. :smile:

thanks all!

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