>Sounds interesting, would you happen to know where I could see a simple
example of a JTAG circuit application or any part numbers of IC's using JTAG
so that I can look up the data sheet.
>Thanks,
>Tim

>JTAG =  Joint Test Action Group.  It is a defined five pin hardware and
>serial communication protocol to primarily allow JTAG equipped complex IC's
>to be daisy chained together and functionaly tested in circuit.  It is also
>used as a programming protocol for some devices.
>Regards
>Mike

JTAG is a lot like SPI. In fact, it has the same reset-clock-data-in/out
connections.  The one I saw ran at 10 MHz.  There may be some kind
of command/data protocol but I think most of the protocol
is specific to the JTAG hardware inside each processor.

It can be used to read out the state of each pin, some or all
registers, and anything else the manufacturer/designer saw
fit to connect it to.  Likewise you can write to these things
to pre set them.  The way JTAG can load a program is by using
memory write cycles to place a program in memory...usually a
loader program.

ARM processors have it.  So did the Pentium II (but not the AMD).
Probably later Pentium chips but I don't know.

Barry

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