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FE5680A Connector Pin-Out

On 2/21/2015, Bob Camp wrote:

Just so it goes into the archives. Here’s the pinout for the FE-5680B with a 15 pin connector on it.

Marking shows as part number 2616000-51604

Pin Function
1 >= +15V power in (likely the same spec as 5680A)
2 ground
3 +5 power in (for some, but not this one)
4 ground
5 RF out (for some, but not this one)
6 spare
7 ground
8 0 to 5V(?) analog tune in (for some but not all, I’d *guess* not for this one)
9 factory use only
10 ground
11 1 pps out (for this one, but not all) lvttl
12 lock indicator (open collector)
13 reset (lvttl input, active high)
14 serial in (lvttl)
15 serial out (lvttl)

Yes, this is in answer to a question Skip asked back in 2009. Replying to that thread might cause something to explode somewhere :)

They seem to be up on eBay for $45 at the moment, along with the info above. No idea if this batch is any good. I haven’t bought any. I’m sure the question of pinout will come up again in about 2 years time. By then the listing and the info will be long gone.


On 3/14/2011 5:09 PM, Dan Rae wrote:

I have just got one of these in from Hong Kong. FEI Part number:
217400-30352-1. It is mounted on a cut piece of PC board. The
seller and three other sellers have different versions of the
connections of these, some, the majority, say that +5v goes to pin 3
but the seller of mine says pin 4.

Answering my own message, with help from others, thanks to them:

This is for FEI Part number: 217400-30352-1 as offered widely on eBay.

Pin 1 is Main supply +15 V, drawing about 1.3A reducing to 0.8 A when warmed up.

Pin 2 is Chassis Ground and power supply return.

Pin 3 is a TTL level logic output: High when out of lock, Low when locked. I don't think putting power into that pin as some vendors indicate would be good karma.

Pin 4 needs +5 V at about 80 mA to produce any output at all with return to pin 2.

Pin 6 has 1 pps.

Pin 7 is 10 MHz output, with 5 the return for that and maybe any data on

Pin 8 and 9, RS232 is not yet checked.

Mine is way out by time nuts standards, it drifts 40 nS in phase compared to GPS in one minute at 10 MHz, and the trimmer on the side does nothing.

I opened it up and could glean little from that, there are obviously many variants of this because there are many alternative links and areas of board unpopulated.


I got a couple of these (FE5680A P/N 217400-30352-1) from a Hong Kong seller, too. Came riveted to a large PCB. I followed some wrong instructions to connect +5V to pin 3, and it even output 10MHz that way (possibly back feed through the ACT240 buffer) for a while until the buffer burned. Replaced it and now feed +5V through pin 4, which is the correct one.

I found a manual at http://www.ham-radio.com/wa6vhs/Test%20equipment/FREQUENCY%20STANDARDS/FE-5680A/5680%20TECH%20MANUAL.pdf which has the correct commands for this unit. Pin 8 receives commands, pin 9 transmits responses. 9600,8,N,1. Basically a 4-byte commnad header with commnad, msglenLSB, msglenMSB,header checksum, data bytes and data checksum. Checksum is a simple xor of all bytes in the header or data portion. Valid commands described in the manual are:


  sample response:  2D 09 00 24 FF FF FE C8 36
 (indicates current offset is FFFFFEC8 or -312, which made the output slower by 2.1e-10 when I calibrated)  

WRITE TEMPORARY OFFSET: 2E 09 00 27 aa bb cc dd cs (aabbccddee is the 32-bit word to write, cs is the xor of aa,bb,cc,dd)

 no response is given to this command, use 2D command to verify. Example command 2E 09 00 27 FF FF FE C8 36

WRITE PERMANENT OFFSET: 2C 09 00 25 aa bb cc dd cs (same as 2E command but also writes to EEPROM)

You would use the 2C command during a calibration (EEPROM life is 100k cycles), and use the 2E command for something like a GPS-trained reference.

C-field potentiometer does nothing for me, adjustment is electronic through the serial port. Mine had a slope of with about 7E-13 (146812 counts for 1Hz change), but don't go overboard - I measured a few setpoints, fitted a curve, set it to the calculated 10.000000000000MHz setting (FFFFFEC8), got it to 2e-12 fo the Z3805 (big grain of salt here - averaging of several 10s gate measurements on a 53312a using a Z3805 reference - broke my measurement and reference stability limits), but turned it upside down and got a 3.7e-11 step change from 2g change. If you are a time nutcase (the type that has 3 cesium clocks but still shows up late to places) tuning it to the last digit, decide where to mount it, first :-)

I am on my second FE5680A P/N 217400-30352-1, also from a the Far East. Both came attached to the PC board with very clever hex drive screws that look like rivets. Please try using an Allen wrench prior to getting out the drill.

precision_timing/fe5680a_pin-out.txt · Last modified: 2015/03/07 09:36 by ko4bb
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