JTAG question

I have a jtag programmer for xilinx devices ,is this a standard interface ?
Can i use this device to program other devices with a JTAG interface (eg
ARM ) ?
Or do i need a dedicated tjag interface for every Jtag device i intend to
use ? (whats the use of a JTAG standard then ?)
Reply to
Sagaert Johan
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The standard JTAG interface is for test (JTAG stands for 'Joint Test Action Group'). The IEEE 1149.1 standard is for that. The 1532 standard [IEEE Standard for Boundary-Scan-based In System Configuration of Programmable Devices (IEEE 1532)] at
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specifies using the JTAG interface in a standard way for such things as ISP FPGAs.
The method used by various cores may or may not actually program that device - often it loads RAM or programs attached flash. There are 'standards' for these interfaces in terms of protocol (ARM uses a particular [wiggler] interface for this and debug functionality, MIPS uses EJTAG, for instance).
At the physical layer, these devices are all roughly the same for the JTAG portion (with the notable exception of TRST on Xilinx and a number of other mfr's devices) but those other functions (accessing internal debug registers for runtime ICE, for instance) requires other pins. ARM requires the reset signal to be operated by the JTAG debugger, as yet another example.
Note that the JTAG standard is a standard. It's all the things built on top of it that aren't.
Reply to
Thanks for the info
I assume that through the JTAG some external flash can also be programmed that has been wired to an ARM device.
interface ?
Reply to
Sagaert Johan
Yes, but you will need specific software for the ARM/Flash device combination you use. Go to
formatting link
and click on one of the advertisement links. They have software for JTAG + ARM that can program a wide range of flash devices for a very reasonable price.
Regards Anton Erasmus
Reply to
Anton Erasmus
The JTAG is actually a back door into the processor core. From its standpoint the Flash chip is an external device.
A complete JTAG cell is able to drive the external lines of the processor chip, but the ARM implementation saves a latch and multiplexer in the cell, and this makes it very difficult, if not impossible, to run the external pins from the JTAG directly.
The rescue is to use the JTAG to load Flash writer code to the system RAM, along with the data to write to the Flash, and start the writer using the JTAG interface. Often the RAM is not large enough, so the Flash image has to be loaded in pieces.
The Flash loader code is very dependent on the memory address space layout in the system and on the Flash chip type, so it usually has to be tailored for the target system.
Been there - done that.
Tauno Voipio
tauno voipio (at) iki fi
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Reply to
Tauno Voipio

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