Using the iMPACT 9.1i software (service pack 01, 02, or 03), there are times when I configure the Spartan-3AN device successfully, but the design does not load. Why does this occur?
This problem occurs because the Mode Select Pins are not properly set.
When Impact 9.1i configures the Spartan-3AN devices, it first programs the internal SPI PROM. After this configuration is complete, a reboot is triggered and the FPGA configures itself from the internal SPI PROM. When the reboot is triggered, the mode pins M[2:0] are sampled. For the configuration to complete successfully, the FPGA mode select pins must be set to M[2:0] = <0:1:1>, which is the Internal Master SPI mode.
If you are configuring from iMPACT and your mode pins are set to JTAG Mode M[2:0] = <1:0:1>, configuration of the FPGA will not complete. To finish configuration of the FPGA, you can simply change the mode pins to Internal Master SPI mode and pulse the PROG pin to trigger configuration, or reconfigure through iMPACT.
In iMPACT 9.2i and later, this problem is fixed. You will have the option to either configure the FPGA directly through JTAG mode or to program the Internal SPI PROM and then configure through Internal Master SPI mode.
For more information on Spartan-3AN configuration, see the "Spartan-3 Generation Configuration User Guide" accessible at:
Click Spartan-3AN and then select "Spartan-3 Generation Configuration User Guide."