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Altera_Forum's avatar
Altera_Forum
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16 years ago

question about jtag

I'm a newer about altera ,and I want to use ep3c fpga,but I have a question about the jtag.when I config the fpga ,I need two jtag ports,one for download sof file to fpga,and the other download pof to eprom,I thought it's too complex,before I turn to altera ,I used lattice,and I need only one jtag port ,it's very simpler,can you get me a simpler solution?

and another question is the vcc of jtag ,I saw in some forum that it's very important,someone said it should be 2.5v,and someone said should be 3.3v,which one is correct?thanks!

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    I guess you're referring to serial flash programming with "second JTAG port"? It's not required, because the flash can be programmed through the FPGA by indirect JTAG programming. The respective circuit in the Cyclone III hardware manual is Figure 9-30 programming serial configuration devices in-system using the jtag interface.

    Altera suggests to use the 2.5V VCCA supply instead a 3.3V VCCIO for the JTAG supply, mainly to reduce the risk of overshoots above the maximum ratings. But the JTAG interface can work with 3.3v according to the device specification. In so far, both are correct.