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msp430f55xx fuse blow question

cody lohse
Intellectual 650 points
Other Parts Discussed in Thread: MSP430F5507

Hi,

I am trying to design up a system that will use the MSP430F5507 in production and would like to blow the fuse to protect the code. Is it possible to blow the fuse through a USB connection? I am assuming no.

Second, what if I design the setup with the D+ and D- lines of the USB connected to the RST and TEST pins, in parallel,  for programming one time and blowing the fuse. I would of course use a modified USB connector and the FET programmer. After the fuse is blown I would use the USB D+ and D- lines as specified for USB communication, but the RST and TEST lines for Spy-Bi programming would still be physically connect to the D+ and D- lines. Would this cause problems when using in USB mode and sending signals to RST and TEST pins on the msp430, or is it that once the fuse has been blown these lines no longer affect the MSP430?

Thanks,

  • 0
    Guru 227245 points

    cody lohse said:
    Is it possible to blow the fuse through a USB connection? I am assuming no.

    Why not. But not directly. On 5x family, the 'fuse' is not physical fuse anymore that neds a blowing voltage (>7V, >100mA for 1ms), but a 'software fuse'. A certain part of the BSL storage area must reporgrammed so it is neither 0xffffffff nor 0x00000000, HTen on next reboot, JTAG will be disabled.
    However, AFAIK the BSL you can access with USB won't be able to do it by itself. So you'll need to enter BSL mode, and upload (to ram) and start some code that does the job.
    Actually, the FET does the same but injects the code through JTAG.

    cody lohse said:
    Second, what if I design the setup with the D+ and D- lines of the USB connected to the RST and TEST pins, in parallel,  for programming one time and blowing the fuse.

    bad idea, since the RST and TEST pins don't like 5V (as they may appear on D+/D-) and TEST should be left open if not used for JTAG anyway. You'd need jumpers to separate them, and then you can as well provide a connector for the FET :)

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