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Using JTAG cable for general comms

Hello,

Is it possible to use a JTAG cable connection to transfer data into and out of an FPGA during regular operations? The situation is like this: we have a Xilinx Spartan 3 board that we are programming with a digilent parallel cable. This works fine. We would also like to transfer data into and out of the FPGA, for which we are currently using serial communications (RS232), but the data rate is now becoming a bottleneck.

The JTAG cable, connected through the parallel port, should be capable of doing much higher speeds than RS232. It is, however, connected to the JTAG pins of the FPGA. Can this somehow be used to transfer data in and out without redesigning the board in any way? Is there any software that could be a starting point for this?

Thanks,

Nitin Chandrachoodan

Reply to
nchandra
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Hi, The following Xilinx Xcell article describes how you can use the JTAG port of a Xilinx FPGA as a general comms channel to a design. One of the uses we have for it is to replace the RS232 as the serial comms channel to designs.

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The example GNAT design can be downloaded for free from here.

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It includes the GNAT design and also supplies some sample TCL illustrating how you can pass data into and out of the FPGA.

Derek

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Reply to
derek

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