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

John Beale beale at bealecorner.com
Sun Jan 29 17:35:31 EST 2012


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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