What is JTAG?

[Spiro]

Ok. I find this:
http://www.ebay.com/itm/Altera-CycloneII-EP2C5T144-FPGA-Board-USB-Blaster-JTAG-/190501213198?pt=LH_DefaultDomain_0&hash=item2c5ac1d40e

I know something about FPGAs but I don't know anything about JTAG. I thought it is something like ICSP but it far more
complicated. This EP2C5T144 device must use external eeprom for internal configuration. Ok. So how do I put conf. in that
eeprom? I presume I could desolder eeprom and program it in dedicated programmer but can I do it trough JTAG?

Why every FPGA maker have it's own JTAG programmer? Is there universal one? What application is used for JTAG programming?
Can I used this USB blaster with this:
http://www.ebay.com/itm/STM32F103VET6-ARM-Cortex-M3-development-Board-JTAG-/200611172216?pt=LH_DefaultDomain_0&hash=item2eb55b8f78

Can somebody explain JTAG in very simple word?

[joelby]

If you stick to the FPGA manufacturer's guidelines and list of compatible devices, you can generally program a connected configuration PROM through JTAG using the standard tools. This is probably the way to go unless you are doing something more complicated (such as allowing programming via an SD card and external microcontroller). Have a look at the schematic diagram for some FPGA development boards.

JTAG is a standardised debugging and testing interface, which can also be used to program FPGAs. It's broadly similar to ICSP. Unfortunately the physical JTAG interface isn't standardised, so you will generally need to get a different JTAG adaptor for different manufacturers.

[Spiro]

On 20 different sites I find 20 different definition of JTAG. What kind of standard is that? 
Probably there is even joke involving JTAG and Chuck Norris. Why there is huge difference in
interfaces prices?

[Neilm]

On 20 different sites I find 20 different definition of JTAG. What kind of standard is that? 
Probably there is even joke involving JTAG and Chuck Norris. Why there is huge difference in
interfaces prices?

Fairly usual for the electronics industry. Don't believe me? Just count how many "standards" there are for serial communication. I'll start - RS232, RS422, RS485, USB ....

Neil

[A-sic Enginerd]

On 20 different sites I find 20 different definition of JTAG. What kind of standard is that? 
Probably there is even joke involving JTAG and Chuck Norris. Why there is huge difference in
interfaces prices?

Fairly usual for the electronics industry. Don't believe me? Just count how many "standards" there are for serial communication. I'll start - RS232, RS422, RS485, USB ....

Neil

Actually, to illustrate the issue even more concise, let's take that first example in your list.
Now, how many different ways have you seen RS232 used? Most only use a subset of all the signals, but which ones? Depends on the need.

To make your searches even more complicated, I'm sure you'll run across tools and boxes and such that are used for development on embedded SOC's. JTAG is used there to control the embedded processor for FW development.

[joelby]

Why there is huge difference in interfaces prices?

I suspect that Xilinx makes 90% of their profits from sales of the USB Platform Cable (it's also a 'smart' cable that contains an FPGA). You can also build a JTAG adaptor for a few dollars using a parallel port, if you have one. Usually if the device is popular enough, someone will make cheaper substitutes (e.g. Digilent) or just clone the original adaptor (see eBay for cheap clone Xilinx and Altera JTAG adaptors).

[maxjtag]

Hi if you want to ding more deeper into JTAG here is a grate site about what is jtag http://jtagprogrammer.com/
best regards Max