Spartan3e Starter kit: External JTag connection ?

[ahz]

Hi all

I'm still using a Spartan3e starter kit for various issues (it's aged but still very usefull).

For my current project i need to program the Spartan using an external uP that i want to connect to the connector for extended JTag (J28).

Now i become unsecure how this should work. The s3e1600 board provides an integrated JTag programmer. Unfortunally it is not documented in the schematic's since it is an Xilinx proprietary design. Moreover J28 does not provide anything like the PGND signal, found i.e. at the Xilinx platform cable USB II. Hence the S3e1600 board can't detect a connected JTag adapter.

I ask myself if this cause any problems when i now use a second (!) JTAG master (via J28) to drive the JTag chain. If i interpret the given schematics correct then i would assume that the integrated JTag controller would be in parallel to J28 (but as i said: this is not documented) which would be asking for trouble .

Can anyone provide some help for this ?

 

Thanks in advance

Regards

AHz

 

[sbobrowicz]

Hey AHz,

The programming circuitry is powered from the USB port it is connected to, so you can be positive that the JTAG pins are not being driven as long as it is not connected to a computer via the USB B port (port J18). In other words, don't connect J18 to a computer and you will be fine.

[JColvin]

Hi AHz,

I've contacted our support team about this and they'll get back to you here on the Forum.

Thanks,
JColvin

[AndrewHolzer]

Hi AHz,

You are correct in your understanding. You'd be double driving the data bus when using the J28 connection in conjunction with the integrated JTAG controller. You should only be using one or the other to drive the JTAG chain.

Andrew

[ahz]

Hi AHz,

I've contacted our support team about this and they'll get back to you here on the Forum.

Thanks,
JColvin

Thanks for your help. I'm waiting curious :-)

Regards

AHz

 

[ahz]

Hi AHz,

You are correct in your understanding. You'd be double driving the data bus when using the J28 connection in conjunction with the integrated JTAG controller. You should only be using one or the other to drive the JTAG chain.

Andrew

Hi Andrew

Thanks for your answer.

My problem is that i have no control over the integrated JTAG controller. Particular i don't know when it is driving. There are JTAG controller in the field that 3-State their outputs when they are inactive. Others keep TDO, TMS & TCK at logic0 (seen at a kind of "on-board programmer" - not really a "official" JTAG controller).

I'm not sure what is 1149-1 conform behavior. Moreover im not sure what is Xilinx conform here

Did i mention that i hate undocumented hardware blocks on lab-boards? ^^

Regards

AHz

[ahz]

Hey AHz,

The programming circuitry is powered from the USB port it is connected to, so you can be positive that the JTAG pins are not being driven as long as it is not connected to a computer via the USB B port (port J18). In other words, don't connect J18 to a computer and you will be fine.

Hi Sam

Ok, that should work perfect for me. Thx a lot for that information.

Regards

AHz