G0MRF/SM6LKM DDS VFO and Jason]

[Andre Kesteloot]

Johan Bodin wrote:

> Hello
>
> I know there are some DDS users/programmers out there!
>
> We have probably not seen the final variant of "sequential single tone
> modulation" yet. So, in order to avoid unnecessary (and painful) PIC
> software changes in the future, I'd suggest that we establish a standard.
>
> It would be very nice if we could agree on a simple serial protocol
> that would allow any PC program, be it DOS or Windoze, to take total
> control over the DDS (I know that Andy G4JNT has done something
> in this direction).
>
> I am in the process of rewriting the PIC software for G0MRF's DDS
> board, a serial input port is on the "todo" list.
>
> If the DDS clock frequency, and possibly also a division ratio and offset
> frequency, is known to the PC software (via a setup menu or whatever),
> the math can be done in the PC, only the DDS phase increment has to be
> sent to the DDS box.
>
> Proposed serial protocol:
>
>    9600 baud, 8N1.
>
>    Only printable ASCII characters are used.
>
>    '=' is used as "start-of-message" character.
>
>    The '=' is followed by eight hexadecimal digits representing the 32-bit
>       phase increment, MSB first! Example: "=0245FD4C3"
>
>    The DDS box changes the output frequency if it receives 8 consecutive
>       valid hex digits after the leading '='. In case of error, it will do nothing
>       but continue putting out the old frequency and wait for a new
>       '=' start character.
>
>    A simple checksum byte (two hex characters) could be added at the
>    end to prevent the TX from exploding if the frequency data should get
>    corrupted from RF interference... Either "vertical parity" (just XOR the
>    bytes) or a modulo 256 sum. CRC seems to be overkill...
>
> (Alberto has indicated that he might add direct DDS TX control to Jason
> if all DDS owners/programmers can agree on a serial protocol)
>
> Please comment!
>
> 73
> Johan SM6LKM