Spartan 2 docs clearly says that, even though
you are configuring the FPGA in serial mode,
you should keep CS pin high.

What about Spartan 3?

I don't see something like:
"Yes, Spartan 2 had an error, but it has been fixed in Spartan 3"

 

OK, when I build my board, I will toggle CS pin (with active WR)
during serial config and will write here.

 

Im sure others are wondering the same thing.

I do not know if there was a change between 2 and 3. Posting your results when you find out would be good of you.

 

I will post, but it will take some weeks... sorry.

 

Here I am!

Well, I did say "some weeks"... (ad infinitum) Am I slow or what?

I've finally done the tests, but with Spartan 3A, not Spartan 3.

First of all, PUDC = 0. (pull-ups during configuration are activated)

1. CS = WR = 0;
throughout the configuration, both CS and WR were constantly 0.

2. CS = 0; WR = toggling;
CS was 0, WR was toggling. (the same as DIN input, actually)

3. CS = WR = toggling;
both CS and WR were the same as DIN.

4. CS = WR = floating;
both pins on FPGA were disconnected.

Result:
Spartan3A was successfully configured in all tests.