User`s manual

High Performance Low Cost Embedded Systems
JTAG Interface
When a development board just comes off from production lines, it is just a bare board without any
data. We will burn the first program to it through the JTAG interface, which is SUPERVIVI. With
SUPERVIVI, we can download more programs and utilities to the board via USB further. In addition,
the JTAG is more often used for debugging. In fact, most of the widely used utilities in markets like
JLINK, ULINK and other simulators actually work via the JTAG interface. A standard JTAG has 4
signals :TMS, TCK, TDI and TDO which are test mode select input, test clock, test data input and test
data output. These 4 signal lines plus a power line and a ground line form 6 lines in total. In order for
testing, most simulators even have a reset signal. Therefore, a standard JTAG is meant to have those
signal lines, and it does not mean whether it is 20Pin or 10Pin. As long as a JTAG interface has those
signal lines, it will be a standard JTAG interface. The mini2440 has a 10Pin JTAG interface which has
complete standard JTAG signals.
Notes: for beginners who just want to focus on Linux or WinCE development, a JTAG interface has
no significance because most development boards already have a complete BSP which includes
commonly needed serial ports, network port and USB port. When a board runs with Linux or WinCE
installed, users can fully utilize more convenient functions and utilities provided by the operating
system to debug. They do not need a JTAG. Even if you can trace your programs it will be extremely
tough to step debug because it will go into the operating system. A JTAG interface might only be
usable for users who do not need to run a complicated operating system or just need a simple
operating system (such as uCos2). Most development boards which already have a Bootloader or
BIOS are completely functional and do not need to be debugged.
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