Any solution to program external 3V powered MSP430 with LaunchPad?

You can try a logic level shifter TXB0304EVM: TXB0304 Evaluation Module  $5.00

Peter

For SBWTCK  you can probably get away with a reverse diode and a pull-up to VCC on the target board, since the clock is unidirectional.

SBWTDIO is trickier, since it is bi-directional. You can try the previously suggested level shifter, or this interesting op-amp solution (p14):

http://www.ti.com/lit/an/slaa148/slaa148.pdf

The circuit is for 5v to 3.3v but it should be trivial to modify it to 3.6v to 3v.

Of course you can always live dangerously and just put a 10k series resistor between the pins, since the MSP430 has clamp diodes that can handle up to 2mA, however they aren't designed for this purpose etc etc which I'm sure you knew already ;)

BTW the 12M crystal on the Launchpad is for the TUSB3410 which acts as a bridge between the PC and the actual "FET" chip the MSP430F1612. Presumably the F1612 just runs on the internal DCO.

Tony

If your circuitry accepts 3.6V and doesn't draw too much current, you may simply connect the LaunchPad VCC and the 3V supply.
Most regulators cannot 'sink' an overvoltage as logn as it is below their input voltage. Effectively, msot regulators limit the current rushing from their input tho their output, so that the output maintains a steady voltage. However, if current is provided from anywhere else, all they can do is 'closing the valve'. and the board rons form the other supply.

Critical are boost regulators or those with internal 'power good' signal that is connected to the CPUs RST pin. (voltage supervisor)

Alternatively, you can connect the LaunchPad signals thorugh a series ressitor of, say, 1k.
the limit of 'VCC+0.2V' is actually nto the limit. The current ist. The current rushing intop any MSP pin must not exceed 2mA rated. This clamp current begins to flow with ~VCC+0.2V. With a series resistor of 1k, a current of 1mA would result in a 1V voltage drop on the resistor and 1 V less on the input pin. Or calculated for 3.6V>3V you will have a current of 400µA and 400mV drop on the resistor. Not exactly low-power, btu that's for the programming cycle only, and the LaunchPad is already USB-powered then :)

Thank you guys. I got the level converter. If it does not work i will use the series resistor.

Please share your results.

thanks

Peter

Well, it not my final report, but i tryed the bidirectional level converter and for some reason it was not working. The reset pin was Low on both sides even with the pull-up. I will have to investigate that further. I also adapted LaunchPad changing R8 to reduce the regulated voltage to 3.3V and it worked. I did not try to reduce to 3V because i was afraid it could not meet the clock requirement. About the 12Mhz crystal, it is connected at MSP430 cystal pins ... it is internally routed to SMCLK pin. Still i belive it is out of specs no?

Reducing Launchpad voltage to 3.3V is not ideal but works with some safety as there are 100 Ohm resistors already placed at the board. Any comment on that?

Regards,

Luis

The 12 MHz crystal controlled oscillator in the MSP430F16xx is used to source MCLK and SMCLK. The SMCLK is also routed to the TIUSB chip which would not work without this12 MHz clock. The 12 MHz MCLK is out of spec.

Port pins of the MSP430F16xx are use directly through a 100R as the SBW signals for the target chip. They are marginal electrically. The timing may be marginal too.

Disclaimer: I am a hobbyist without any training in engineering. All my posts in this forum are based on my own hunches void of authoritative doctrines.

old_cow_yellow said:

The 12 MHz MCLK is out of spec.

But with a /2 divider on MCLK, the 12MHz can still be used for SMCLK and forwarded to the TUSB. And this likely is what the original firmware on the 1612 does: using the 12MHz crystal as source for SMCKL for output, and as source /2 for 6MHz MCLK operation. But that's just a guess.

Still, 12MHz or th ecrystal are outside the specs for XT2 input. But chances are that with a carefully chose crystal, it will work flawlessly anyway. The 8MHz limit is most likely due to the CPU core limit and not a hard limit for the oscillator circuit. However, 3.3V might be needed to make it work, since CMOS circuitry works faster on higher voltages.

Jens-Michael Gross said:

... But with a /2 divider on MCLK, the 12MHz can still be used for SMCLK and forwarded to the TUSB. And this likely is what the original firmware on the 1612 does: using the 12MHz crystal as source for SMCKL for output, and as source /2 for 6MHz MCLK operation. But that's just a guess...

They could have done that. But I think they did not and use /1 for both MCLK and SMCLK.

OCY said:

But I think they did not and use /1 for both MCLK and SMCLK.