Hi,
Here's something that may get you started. Obviously you need to set the correct baudrate and change the size of the array to match the maximum number of bytes that may be transfered (now set to 16).
Code:
'Set baudrate for USART
DEFINE HSER_BAUD 2400 

'Set up an array of 16bytes to use as storage for the data.
myString VAR BYTE[16]


'Wait for $52 and $E0 and then store the next 16 characters in the array 
'myString. Terminate if $FD (End of message) is recieved before we have 
'16 characters in myString. $52 and $E0 are default TX and RX adresses, 
'change if needed.

HSERIN [WAIT($52,$E0), STR myString\16\$FD]
You now have the data stored in the myString array. The first byte is the CN byte so if that byte is $00 then the datafield (from byte 3 and forward, to the last byte or the byte containing $FD) contains the frequency.

Hope it helps.

/Henrik Olsson.