Can we update firmware in microcontroller using JTAG? If so ,other than hardware adapter(jtag,synchronous)and bootloader(software programming,asynchronous) what is the difference between these two.
Can we update firmware in microcontroller using JTAG?
It depends on your microcontroller. See its data sheet and other documentation.
What is the diffrence between JTAG and bootloader programming in microcontroller?
The JTAG interface is a hardware based method. You might look at it as if you can access internal control lines, for example to write or read specific memory cells. No software is involved on the microcontroller's side. The JTAG standard defines a serial interface on a very low level.
Bootloader programming needs a small application in the microcontroller: the bootloader. It might use any hardware interface (like a serial line) and any protocol, for example to access internal flash memory. Some microcontroller are sold with a bootloader.