Re: JTAG question

Sagaert Johan wrote:
> 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 ?)
>
> Johan

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
http://grouper.ieee.org/groups/1532/ 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.

Cheers

PeteS

.

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