[time-nuts] FE-5680A command decoding speculation

[Bob Camp]

Hi

Unlike a GPSDO, a rubidium does not have a reference to construct a table against. If they are doing temperature correction, it would run on a factory loaded table.

Bob



On Jan 29, 2012, at 5:35 PM, John Beale <beale at bealecorner.com> wrote:

> Speculation... just for fun.
> 
> Seeing Javier's great recent work on the 5680 DDS operation has me thinking more about two of the mystery commands.  If the unit is applying a periodic correction to the DDS frequency beyond what the user requests via RS-232 commands, as a function of (for example) temperature, and/or a power supply voltage, it would need some calibration coefficient. Those correction factors would logically be a user-settable parameter. We know there is a 12-bit 4 channel A/D chip onboard, apparently monitoring temperature (and supply voltage?) and maybe that's not just a passive monitor function, but used to generate the correction factor.
> 
> Now, looking at the response to Cmd 0x57 and 0x59 on my unit, I see a long string of bytes which look like sets of 2-byte pairs, the second byte of each pair differs by roughly the same number from the previous. Each unit has a different number of these pairs, and they are followed by all 0x00 bytes.
> 
> Pure speculation here, but if the unit was keeping a log of the most recent commanded voltage or temperature coefficient correction factors, and this was done at regular intervals, it might look a lot like that.  Another possibility is an automatically generated correction, if there is any known drift with time (?).  Yet another possibility is a look-up table, for example, to take the measured temperature to find the right DDS offset correction factor.  I might expect the lookup table to be a consistent size, though.
> 
> In case of interest, below is the data I'm talking about, from my three units. Remember the first 4 reply bytes is a command header, and the last byte is a checksum.
> 
> FE-5680A Unit Number 62388:
> ----------------------
> Cmd 0x57 0x56 byte reply: 57 56 00 01 30 40 00 4B 00 58 00 63 00 6E 00 7A 00 85 00 90 00 97 00 9C 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0A
> 
> Cmd 0x59 0x56 byte reply: 59 56 00 0F 30 BF 00 A2 00 80 00 2F 00 00 00 EA FF 9E FF 7C FF 4A FF 39 FF 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 06
> 
> FE-5680A Unit Number 66721:
> ----------------------
> Cmd 0x57 0x56 byte reply: 57 56 00 01 50 41 00 43 00 47 00 4A 00 4E 00 51 00 55 00 58 00 5C 00 5F 00 63 00 66 00 6A 00 6E 00 71 00 75 00 78 00 7B 00 7F 00 82 00 85 00 89 00 8C 00 90 00 93 00 97 00 9A 00 9E 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 A5 
> 
> Cmd 0x59 0x56 byte reply: 59 56 00 0F 50 CB FF BC FF C6 FF B0 FF B5 FF A9 FF 8E FF 77 FF 9B FF B0 FF 8C FF CD FF E5 FF 00 00 81 FF B0 FF C1 FF D6 FF DD FF D2 FF D9 FF B7 FF D8 FF CB FF E4 FF DB FF F9 FF E1 FF 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 B7
> 
> FE-5680A Unit Number 72476:
> ----------------------
> Cmd 0x57 0x56 byte reply: 57 56 00 01 68 3F 00 42 00 46 00 4A 00 4D 00 51 00 55 00 58 00 5C 00 5F 00 63 00 66 00 6A 00 6D 00 71 00 74 00 78 00 7B 00 7F 00 82 00 86 00 89 00 8D 00 90 00 94 00 97 00 9B 00 9E 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 E6
> 
> Cmd 0x59 0x56 byte reply: 59 56 00 0F 68 FF FF 01 00 E3 FF CE FF D8 FF EA FF D2 FF F0 FF FE FF 16 00 0A 00 0D 00 F6 FF 00 00 EF FF FE FF DD FF D3 FF E2 FF F5 FF F2 FF F3 FF E5 FF EE FF B3 FF C4 FF DA FF A9 FF 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 4B
> 
> ---
> John Beale
> n8juf
> 
> 
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