I'm designing a circuit for configuring 4 Spartan-3E FPGA from an Atmel AVR microcontroller.
I want to configure the FPGA in slave serial mode. Because of the difference in the supply voltages, there are some different logic voltages, some 2.5V, some 3.3V
AVR 3.3V FPGA VCC0 3.3V FPGA VCCAUX 2.5V
Xapp453 states that CCLK needs to be driven with 2.5V logic, however, the Spartan-3E datasheet states (Page 68) that CCLK is powered by VCC0_2 which will be 3.3V.
I'm guessing that the contradiction is due to XAPP453 being for Spartan-3, not Spartan-3E.
I just need to know if CCLK needs the logic level changing as well the PROG_B signal.
Could someone just check the following for me:
PROG_B driven by AVR needs to be 2.5V logic DIN driven by AVR 3.3V logic (I think) CCLK driven by AVR 3.3V logic
INIT_B driven by FPGA 3.3V logic DONE driven by FPGA 2.5V logic DOUT driven by FPGA 3.3V logic
Many thanks Andy