Honda Radio ask for code.

I got used Honda Odissey and one day that I disconnet the battery the radio can not turn on, this asked for a code.

How can I get this code to can turn on the radio?

The honda is 1999 model year.

I just bought an 2004 Odyssey also. It shows CODE on the radio. At the dealer, the guy went into the glove compartment and looked up the number. In my van there was a white label inside the glove compartment and he used the shorter number!!!! Then it's free. However, if your car doesn't have any number (i.e. look around but start with the glove compartment), then the dealer can look up like the serial number of the radio or from the VIN, call the HONDA office and get the code if that is the OEM radio. This costs $5 in Long Beach, California.

My 2000 came new with a plasic card (credit size) with the numbers on it.
If u got it from the original owner ask for the card.
If u got it from a dealer, they owe u the code - their nickel.