When running a Spartan-3 device via SMAP at low temperatures with a Platform Flash, DONE may not go high. If this occurs, the status register read from the FPGA after a configuration is attempted will be the same as that of a blank device.
The Platform Flash data sheet and user guide provide layout diagrams for different configuration modes. The SelectMAP configuration diagrams have a 1k pulldown on the CS_B and RDWR_B lines of the FPGA. These pulldown values may not be strong enough when configuring a Spartan-3 at low temperatures. These signals can just be tied to ground or pulled down with a 100 ohm pulldown.
This has been seen to cause problems in only a couple of systems with the Spartan-3 device. This device has internal pullups that are stronger than most devices and it is the strong internal pull value that has been seen to cause problems at very low temperatures. For most systems, this is not an issue and is primarily targeted at Spartan-3 devices running SMAP at low temperatures.
This applies to figures 9,10,11, and 13 in the Platform Flash Datasheet (DS123, v2.11.1, March 30, 2007), and the recommendation will be changed in the next revision of the data sheet.
Figures 5-2, 5-3, and 5-4 in the Platform Flash PROM User Guide (UG161, v1.0, August 17, 2005) will also be modified.
RDWR_B and CS_B should be tied to GND or pulled down with a 100-ohm pulldown.
The recommendation for existing systems is to leave the pulldown resistors if they are in place, unless the device is a Spartan-3 being configured at low temperatures.