Time TMS Goes Low After POR
TMS
I
TF
I
TEST
MSP430G2744, MSP430G2544, MSP430G2444
SLAS892C – MARCH 2013 – REVISED SEPTEMBER 2014
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6.19.19 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, I
TF
, of 1 mA at 3 V, 2.5 mA at 5 V can flow 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 again taken 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
TMS is 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 flows only when the fuse check mode is active and the TMS pin is in a low state
(see
Figure 6-1
). Therefore, the additional current flow can be prevented by holding the TMS pin high
(default condition).
Figure 6-1. Fuse Check Mode Current
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.
68
Detailed Description
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