In this
post I am going to explain how to disable JTAG. The JTAG stands for Joint
Test Action Group(JTAG), Which is an international standard method for
testing the microcontroller performance and delay calculations. Therefore, most of the microcontrollers are having this facility to test and debug by the
programmer. This is done by four signals namely TDI (Test Data Input), TDO (Test
Data Output), TMS (Test Mode Select) and TCK (Test Clock). It is important to know how to disable JTAG
because the JTAG is enabled while the microcontroller shipping which makes the
port pins occupied by the JTAG signal do not work properly. For example, in ATmega16 microcontroller, in which the JTAG pins are occupied with
PORTC. Which are PC5, PC6, PC7 and PC8. So
you cannot use this pins for any port operation. You can disable JTAG using
Fuse pins but it is not a good practice. The best way is to write a “1” to JTD
bit of MCUCSR register of you AVR microcontroller as shown below code.
MCUCSR =
(1<<JTD); // Disables JTAG pins
MCUCSR =
(1<<JTD); // Disables JTAG pins
Sometimes you have to write this code twice
for proper working
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