Serial console not showing anything at boot time

I have a RB2011UiAS-2HnD-IN router and have set up a connection from the RJ-45 serial port to COM1 on my computer.

I have minicom set up for /dev/ttyS0 (COM1) at 115200 baud 8N1. When characters are typed in minicom they are echoed
correctly to the screen so the serial port appears to be working OK (I have echo turned off, I checked).

However when I power up or reboot the RB2011 it stays for a long time with “routerboot configuration” displayed on the LCD
but nothing displays in minicom on my computer. Eventually it times out and the normal boot process proceeds.

Can anyone suggest how I can get the console boot menu working?

I have not try with minicom but this is what i have try and publisched on my website.
http://www.wirelessinfo.be/index.php/mikrotik/pages/seriale