Datasheet

MSP430x12x
MIXED SIGNAL MICROCONTROLLER
SLAS312C − JULY 2001 − REVISED SEPTEMBER 2004
32
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
JTAG fuse check mode
MSP430 devices that have the fuse on the TEST terminal have a fuse check mode that tests the continuity of
the fuse the first time the JTAG port is accessed after a power-on reset (POR). When activated, a fuse check
current, a fuse check current, I
TF
, of 1 mA at 3 V, 2.5 mA at 5 V can flow from from the TEST pin to ground if
the fuse is not burned. Care must be taken to avoid accidentally activating the fuse check mode and increasing
overall system power consumption.
When the TEST pin is taken back low after a test or programming session, the fuse check mode and sense
currents are terminated.
Activation of the fuse check mode occurs with the first negative edge on the TMS pin after power up or if the
TMS is being held low during power up. The second positive edge on the TMS pin deactivates the fuse check
mode. After deactivation, the fuse check mode remains inactive until another POR occurs. After each POR the
fuse check mode has the potential to be activated.
The fuse check current will only flow when the fuse check mode is active and the TMS pin is in a low state (see
Figure 13). Therefore, the additional current flow can be prevented by holding the TMS pin high (default
condition).
Time TMS Goes Low After POR
TMS
I
TF
I
TEST
Figure 13. Fuse Check Mode Current, MSP430F12x
NOTE:
The CODE and RAM data protection is ensured if the JTAG fuse is blown and the 256-bit bootloader
access key is used. Also see the bootstrap loader section for more information.