Hello is there any core to communicate a Digilent Spartan 3E with my laptop through RS232?
Thank you.

Dear Mike,
Jes it is. You can find it on tfe digilent resources site - https://reference.digilentinc.com/reference/programmable-logic/spartan-3e/start?redirect=1. How to use it You can find it in my project about Present enxryptor/decryptor.

Best regards,
Krzysztof

Hello, I followed the link + the files.

I made a constraints file:

NET "LEDS(7)" LOC = "F9" | IOSTANDARD = LVTTL | SLEW = SLOW | DRIVE = 8 ;
NET "LEDS(6)" LOC = "E9" | IOSTANDARD = LVTTL | SLEW = SLOW | DRIVE = 8 ;
NET "LEDS(5)" LOC = "D11" | IOSTANDARD = LVTTL | SLEW = SLOW | DRIVE = 8 ;
NET "LEDS(4)" LOC = "C11" | IOSTANDARD = LVTTL | SLEW = SLOW | DRIVE = 8 ;
NET "LEDS(3)" LOC = "F11" | IOSTANDARD = LVTTL | SLEW = SLOW | DRIVE = 8 ;
NET "LEDS(2)" LOC = "E11" | IOSTANDARD = LVTTL | SLEW = SLOW | DRIVE = 8 ;
NET "LEDS(1)" LOC = "E12" | IOSTANDARD = LVTTL | SLEW = SLOW | DRIVE = 8 ;
NET "LEDS(0)" LOC = "F12" | IOSTANDARD = LVTTL | SLEW = SLOW | DRIVE = 8 ;

NET "CLK" LOC = "C9" | IOSTANDARD = LVCMOS33 ;

NET "RST" LOC = "L13" | IOSTANDARD = LVTTL | PULLUP ;

NET "RXD" LOC = "R7" | IOSTANDARD = LVTTL ;
NET "TXD" LOC = "M14" | IOSTANDARD = LVTTL | DRIVE = 8 | SLEW = SLOW ;

Is it correct?

Using LEDs is not compulsory for use with RS232, so you can use it
only for testing purpose. In that case you have to use pointy brackets
rather than parentheses, so use "LED" than "LEDS(0)".
Another thing is the reset button. In S3E500 board is connected to the
slide swithes which is not convienient to use as reset button. It is
better to use push button (i.e. button south, K17 ->
NET "BTN_SOUTH" LOC = "K17" | IOSTANDARD = LVTTL | PULLDOWN ;)
The rest seem to be ok.