USB blaster download cable -- Data rate on 10-pin connector

[Altera_Forum]

On the USB based Blaster download cable to program the Altera FPGA, we would like to know the Data Rate of signals while programming the FPGA.  

  We are in need of this support information in order to decide what kind of extensions we can make from the 10-pin flat (FRC) cable. In a system we are building, we need to have access to the FPGA board that is sitting inside a big box. Can we extend the FRC cable by another 15 or 20 inches by an extension cable? Will it affect the programming functionality of the USB Blaster cable?

[Altera_Forum]

The JTAG clock speed of USB Blaster is 6 MHz (fixed). Another 20 inches isn't a problem of clock speed, but may possibly cause more signal overshoot or even double clocking by distorted TCK edges.  

 I'm using extended JTAG cables occasionally, but the system boards have mostly series resistors and clamp diodes, I can't guarantee that it works with your boards as well.  As an additional observation, the AS programming interface is more sensitive to signal quality issues than JTAG.

[Altera_Forum]

Extending the JTAG cable may work for programming if you're in a fairly clean environment and extend it with good quality cable. 

 If you are using a longer running program such as the Nios II debugger, SystemConsole, nios2-terminal etc then it will be more affected by errors as it's running for longer (hours or minutes as opposed to tens of seconds).   You may want to consider extending the USB cable if that's possible as that is differential so more resistant to errors.