MSP430F2370 JTAG Reset

To attach a debugger to a running device using JTAG, it is obvious that it may not use RST, as this would reset the processor and end program execution. Since this is possible and supported by seom debuggers, it mus tbe possible to use JTAG without RST.

But the programming tools generally reset the device before and usually after starting the programming. This ensures that all internal hardware is in a known configuration and won't interfere with the programming process.

Many devices with more pins do not have a TEST pin, as this pin just switches the shared port hardware from I/O to JTAG. These processors have dedicated JTAG pins, so a TEST pin is not necessary as these pins are configured for JTAG already. The new 54xx processors, despite of having 80/100 pins, do have a TEST pin again, as the JTAG port can be used as normal I/O if not needed.

I'm not sure that you've really answered the question.  Saying that the programmers generally reset the device is not the same as the programmer must reset the device.  Just because the debugger can't use reset during the JTAG session is not the same as the process of attaching to a device does not require a reset.  Do you have actual experience with this class of part, and not connecting reset to the programmer?

I have an MSP-FET430UIF I'm trying to program an MSP430F2370.  Do I need the reset pin attached to the programmer to reset the device to ensure the internal hardware is in a known configuration?  Or will the programming process do that independent of having the reset pin attached?  Since it's a BGA device (requires more expense board spin and population costs) I'd rather not go through an extra spin to find this out rather than asking the question.

Thanks,

Greg

Well, there is no yes/no answer for your question. The answer is: it depends.

You misunderstood me. The debugger can attach to a runing device without resetting ist (letting it continue running uninterrupted until you want to), so for establishing a JTAG connection, there is no access to RST needed. This corresponds with what Brandon said: The (4-wire) JTAG connection itself does not require RST.

The programmer software, however, might. I know that the msp430-jtag.exe always resets the device before beginning the programming process (and after, to start the new firmware). And it will complain (and fail to continue) if reset won't work. So this software definitely requires access to the RST line. I guess this is because for the programming process, the software needs to identify the processor, so it know which algorithm to use/which flash controller is there, where the RAM is to place the flashing codelet to etc. Maybe if you just tell the software which processor shall be assumed to be connected, it does not need to check and maybe will work without resetting the device. It depends on how it has been programmed.

You can check yourself. If you have the FET430UIF, you most likely also have a demo board with processor. You can just cut the RST line from board to FET and check whether it still works. If so, fine., if not, then not. In any case you'll get your answer.

Thank you.  This is (to me, at least) much clearer.  It's also what I was afraid the answer might be, since I do need to program the device.  Unfortunately, all of my demo boards use Spy-By-Wire, so I can't test it.  The only reason I'm going to JTAG is to use the BGA package.  I have to fit this in a very small space and use a spring contact system to program the device. I was hoping to get away with one less line since to place this I need to bump up the from the desired form factor.

Thanks,

Greg

You can try to go for the bootstrap loader that is in every MSP device for programming.

This way you'll need RST, two port pins (RX/TX, device dependent) and I think the test pin. That's only 4. You can even connect the two BSL port pins with hardware RX/TX lines of one of the UARTs, so you have a serial line available for debugging output. It might even possible to triple the lines with the JTAG pins, so JTAG is still available. All port pins are inputs on power-up, so they don't disturb each other. Depending on the adapter you connect to these 4 pins, you might have a serial connection to the PC for either looking at debug output or BSL, or connect the JTAG interface and do debugging sessions (but then, you should not enable the UART RX/TX pins in your software. Set a breakpoint on the PSEL instruction and skip it in the debugger)