How do I boot 6.0-BETA2 iso with rs232 console?

[Dieter]

> AMD64 machine, booting
> -r--r--r--  1 root  wheel  50087936 Aug 22 17:57 6.0-BETA2-amd64-bootonly.iso
> from a dvd.
> 
> Console is rs-232, 19200 baud.

I finally figured out to type "boot -h" at the okay prompt,
and then it starts printing the usual info about devices found,
at the wrong baud rate.

How do I set the baud rate?

It then gets to

	ATA PseudoRAID loaded
	Trying to mount root from ufs:/dev/md0

and hangs.  No response to the keyboard.

Now what?