Is there a way to prevent code being read from an MSP430 without blowing the fuse?

Question

I was recently involved at a project in a small company where we had fears of someone taking the code from the master chip, an MSP430F2419, and using it for a competing product. We ended up blowing the JTAG fuses for the first few beta releases, but because of the blown fuses we could not reprogram them. Is there a middle ground between blowing the JTAG fuse that will prevent someone from reusing the code on the chip, but let us reprogram the chip?

Answer 1

MSP430Fxx microcontrollers can be programmed via the JTAG or Spy-Bi-Wire Interface as long as the Security Fuse is not blown! When the Security Fuse is blown as in your case, then the MSP430Fxx microcontrollers can still be accessed, but only via the BSL Interface. For an example C source code and project files, have a look at here: SLAU320

JTAG is locked by programming a certain signature into the devices' flash memory at dedicated addresses. The JTAG security lock key resides at the end of the bootstrap loader (BSL) memory at addresses 0x17FC to 0x17FF. Any value other than 0 or 0xFFFFFFFF programmed to these addresses irreversibly locks the JTAG interface.

Because the JTAG security lock key resides in the BSL memory address range, appropriate action must be taken to unprotect the memory area before programming the protection key.

Answer 2

You may use MSP430 family Boot Strap Loader (BSL). See http://www.ti.com/lit/ug/slau319h/slau319h.pdf.

In the default protocol, reading flash blocks are password protected. Also, you can implement your own bootloader according to your needs.