Hi everyone. As I'm making a CPLD board for the XC9572 5V CPLD from Xilinx I would like to know if it's possible to program this with a 3.3V compliant JTAG programmer from Digilent? I mean, does the JTAG signals have to be 5V, if the chip is powered from a 5V source? Or can the JTAG signals be 3.3V, if I fx power the JTAG adapter from a 3.3V source and then connect the signals to the JTAG pins on the CPLD? Best Regards Thomas Jespersen
> Or can the JTAG signals be 3.3V, if I fx power the JTAG adapter > from a 3.3V source and then connect the signals to the JTAG pins > on the CPLD? As the DS does not state a difference between 3V3 and 5V VccIO you will be able to use the 3V3 JTAG programmer:
VIL Low-level input voltage 0 0.80 V VIH High-level input voltage 2.0 VCCINT + 0.5 V
But be aware that the the TDO will be a 5V output signal. You must adapt this to the needs of your programmer.
Hmm, so would this schematic work? http://elec.tkjweb.dk/blog/wp-content/uploads/JTAG_ConverterAdapter.pdf
As I mentioned, the only signal of interest is the TDO signal. And here i would give a try to a simple voltoage divider to convert the 5V TDO from the CPLD to the 3V3 level of the programmer. With the values 330 Ohm (from CPLD TDO to prog) and 680 Ohm (from the prog to GND) I would the thing expect to work.