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Xilinx JTAG Schematic

Started by Mark Higgins April 22, 2006
I'm a complete noob to the ARM controllers. I picked up an AT91ARM7S
256 and I'm making up a prototype board of my own. I'd like to make
up a DIY JTAG as well. Will this Xilinx schematic work with WinARM
or GNUARM? I've seen other schematics that are based on the 74HC244,
like the one in the files section of the Yahoo group, but I've
already thrown this into Eagle, and I already have the 74HC125 chip,
so I'm hoping this one will work out with a minimum of changes.

http://www.higginstribe.com/gallery/jtag/xilinx_rev2.pdf

Thanks for any answers.

Mark Higgins
Mark,

The schematic you attached was for a download cable, not a target PCB.
What that your intent?

Chip

--- In A..., "Mark Higgins" wrote:
>
> I'm a complete noob to the ARM controllers. I picked up an AT91ARM7S
> 256 and I'm making up a prototype board of my own. I'd like to make
> up a DIY JTAG as well. Will this Xilinx schematic work with WinARM
> or GNUARM? I've seen other schematics that are based on the 74HC244,
> like the one in the files section of the Yahoo group, but I've
> already thrown this into Eagle, and I already have the 74HC125 chip,
> so I'm hoping this one will work out with a minimum of changes.
>
> http://www.higginstribe.com/gallery/jtag/xilinx_rev2.pdf
>
> Thanks for any answers.
>
> Mark Higgins
>
--- In A..., "Mark Higgins" wrote:
>
> I'm a complete noob to the ARM controllers. I picked up an AT91ARM7S
> 256 and I'm making up a prototype board of my own. I'd like to make
> up a DIY JTAG as well. Will this Xilinx schematic work with WinARM
> or GNUARM? I've seen other schematics that are based on the
74HC244,
> like the one in the files section of the Yahoo group, but I've
> already thrown this into Eagle, and I already have the 74HC125 chip,
> so I'm hoping this one will work out with a minimum of changes.
>
> http://www.higginstribe.com/gallery/jtag/xilinx_rev2.pdf
>
> Thanks for any answers.

It all comes down to what you want to do.

JTAG from a PC to a target will work with the same interface, however
you need to make sure that the host side software uses the same
parallel port pins for the same purpose. To verify this, search
Google or whatever for Wiggler clone schematics. If you are using an
open source debugger then youy also have the option to reconfigure
things to use the Xilinx cable.

You have not said what Xilinx part you're using and how you want to
drive it. If you always want to program the Xilinx from a host (PC),
then you can, in theory, just hook up the two jtags into one jtag
chain (there's a Xilinx app note on doing this) and thus cut down on
connectors.

If, however, you want to program the Xilinx from the micro then you
need to hook up the Xilinx JTAG pins to micro port pins instead. This
is a very handy thing to do, IMHO, as it provides flexibility in
allowing you to change the Xilinx firmware down track.
I don't know the answer to your question regarding the '244. My
solution has been fairly simple:

1 - I purchased the IAR Kick-Start package (~$300) which includes a
Segger J-Link debugger and a 32k-limited version of the IAR ARM
toolchain

2 - I downloaded the free version of the Xilinx ISE toolchain (v8.i)

3 - I purchased a dev kit from Xilinx (<$100) which contains a
download cable (DB25 - SIP6) which I believe is the equivalent of the
schematic you posted. I actually purchased 2 kits for ~$115 (one
CPLD & 1 FPGA) both of which included the download cable. I only
needed to purchase 1 kit but I can't recall the individual prices.

The results have been excellent, the only drawback is that I have 2
debug/download connectors on my target PCB (1 20-pin for the J-Link,
1 6-pin for the Xilinx), but this is only temporary during the
development phase of my project.

I was able to get my target hardware (AT91SAM7S256, XC2S30-5VQ100C
Spartan-II) up and going on the first try. The only mistake I made
was fogetting to put VCC on pin 6 of the SIP6 PCB jack. With that
one exeption it was literally 'plug-and-play'.

This has saved me days/weeks of stumbling around trying to glom
together various disparate 'home-grown' or otherwise unsupported
tools/hardware. I was also able to use the schematic/layout of the
AT91SAM7S-EK dev board (which comes with the $300 IAR kit) to select
capacitor types, values and layout around the AT91 CPU. I don't know
how much that helped, all I know is the 1st time I plugged in the J-
Link debugger my target came up immediatly. 'Nuff said?

I would also note that using established tools at the outset shortens
your learning curve enabling you to build a body of knowledge to
support the use of WinARM/GNUARM tools later on. In particular if
you cannot afford the typically ~$3k ARM toolchains (IAR's is $2,995)
using the intro dev tools I mentioned (IAR/Xilinx) will get you well
prepared for using the generic tools later on.

Lastly, I've found multiple problems with flashloaders and other
debugging tools that would have been impossible to decipher without
the support if the IAR FAEs. Perhaps the equivalent publicly
available 'free' resources are bug-free, but I doubt it.

Hope this has been helpful. If you have additional questions or if I
can be helpful on other ways feel free to e-mail me directly (I
assume you can see my e-mail address)

Chip

Memfault State of IoT Report