Moving from a MSP430F1121A to a MSP430F2121

While the two chips us an almost identical layout and the 2121 can be used as replacement for the 1121 in an existing PCB, the two devices are internally not identical.

You cannot simply upload an old binary image to the new chip. You cannot even just recompile the source code. The clock system is different and there are other differences too that require at least some changes in the source code:
P2.6 and P2.7 are now available as alternative for the external crystal X1.
X1 is active by default, but configuring P2 may disable it.
There are more comparator inputs available, also the comparator is slightly different.

And finally, the 2121 doesn't seem to support SpyByWire. Not all 2x family devices do. Especially the older ones don't.

However, you can now run with up to 16MHz and do so from DCO (the 1121 was limited to 8MHz and the DCO didn't run faster than ~6MHz)

Well, smell... does anyone have a suggestion for 1121/comparator (the comparator is the only feature the code uses) that works with SpyByWire?

I only had 2 more pins to the outside world and wanted to debug/calibrate in the field...

Thor Johnson1 said:

does anyone have a suggestion for 1121/comparator that works with SpyByWire?

The 2121 was built as pin-compatible 2x family replacement of the 1121A. So you can replace the 1121A on existing PCBs. And since the 1121 didn't have SBW and therefore existing 1121 PCBs don't support it, it makes no sense to have it on the replacement chip. (well, you could go and abuse any existing 4-wire JTAG signals on an existing JTAG connector as normal GPIOs then, and I think that's what you try to do, but that contradicts the idea of a pin-compatible replacement)

For new PCBs, you can pick any one of the 2x family that has SBW and a comparator. Use the TI product selector to find what you need.

Alternatively, you can use the two pins you have and implement a software UART/I2C to communicate with the chip and your firmware, then receive data and send commands for your calibration. But this will require support of this inside your firmware. And a frontend program on PC (in case of a software UART, it could by PUTTY or HyperTerminal).

I don't use CCS or IAR and therefore no debugger for my projects. I usually implement debug output or even a command interface with a serial connection.

Is there a way to check spy-by-wire in the selector?

Since spy-by-wire uses the rst/nmi pins, I figured that it was "compatible"....

Thor Johnson1 said:

Is there a way to check spy-by-wire in the selector?

Apparently not. Too bad.

However, there's another option: the G2 LaunchPad supports only SBW and only 2x family. So checking the devices you can program with the LaunchPad (see the LaunchPad Wiki) gives you the list of 2x Devices with SBW capability.

Since spy-by-wire uses the rst/nmi pins, I figured that it was "compatible"....

Well, all MSPs have an RST pin and many have a TEST pin, long before SBW was introduced. SBW was implemented to reduce pin usage for JTAG access. The pins are not an indicator for SBW support.