What is JTAG? - Page 1
Forum section: electronics / beginners

author: Spiro
author_rank: Contributor
timestamp: November 22, 2011, 02:57:25 am
content: Ok. I find this:http://www.ebay.com/itm/Altera-CycloneII-EP2C5T144-FPGA-Board-USB-Blaster-JTAG-/190501213198?pt=LH_DefaultDomain_0&hash=item2c5ac1d40eI know something about FPGAs but I don't know anything about JTAG. I thought it is something like ICSP but it far morecomplicated. This EP2C5T144 device must use external eeprom for internal configuration. Ok. So how do I put conf. in thateeprom? 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=item2eb55b8f78Can somebody explain JTAG in very simple word?

author: joelby
author_rank: Frequent Contributor
timestamp: November 22, 2011, 04:50:45 am
content: 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.

author: Spiro
author_rank: Contributor
timestamp: November 22, 2011, 01:37:39 pm
content: 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 ininterfaces prices?

author: Neilm
author_rank: Super Contributor
timestamp: November 22, 2011, 06:41:57 pm
content: Quote from: Spiro on November 22, 2011, 01:37:39 pmFairly 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

author: A-sic Enginerd
author_rank: Regular Contributor
timestamp: November 22, 2011, 09:49:50 pm
content: Quote from: Neilm on November 22, 2011, 06:41:57 pmActually, 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.

author: joelby
author_rank: Frequent Contributor
timestamp: November 23, 2011, 02:06:29 am
content: Quote from: Spiro on November 22, 2011, 01:37:39 pmI 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).

author: maxjtag
author_rank: Newbie
timestamp: September 01, 2012, 09:27:57 pm
content: Hi if you want to ding more deeper into JTAG here is a grate site about what is jtaghttp://jtagprogrammer.com/best regards Max