PIC sniffer ...

Hello, I am not sure that the Tittle is the exact term , but
let me explain
I have the drawing (a 16F628 sending datas to a synthetiseur ADF4110)
so I know which pins are used (datas, clock, enable)
I have the HEX file
I try to desassemble it, I got all the ASM code, but I am not enough fluent !

my need is to know what are the values (20 bits format) that are send to the
ADF4110.
Initialisation register
Latch register
for the divider registers, it is not a problem

What can be done ? software tool or hardware sniffer ?

Thanks
Francois F1CHF