[time-nuts] BC637PCI 1024 week rollover

GandalfG8 at aol.com GandalfG8 at aol.com
Sun Feb 9 16:23:27 EST 2014

It may be that your onboard batteries are in better health than mine are,  
although mine might have been disabled using the software, as I tried 
booting up  without an antenna this evening and got the right year this time but 
twith he  date as 1st January:-)
What I found when running in GPS mode was that I could correct the date but 
 it would get overwritten again.
As I commented in my previous reply to Magnus' comments, I still don't  
understand why units produced after 1999 should have this problem anyway.
Thanks for the data, I'll keep that and compare later, and I'll be very  
interested to hear how yours performs once the antennna is connected.
Running off 1PPS is an option but I'd much prefer to use actual GPS time if 
 possible, unfortunately, as commented earlier, the problem lies with the 
BC637  itself, not the GPS module.
Your mention of other GPS modules reminds me that the appropriate set  of 
schematics for these BC637s shows that a header swap would allow the board to 
 use a Motorola Oncore in place of the Trimble ACE2 or ACE3. Not sure that 
I'll  ever try that but it might help explain why they take the raw GPS  
data rather than what's already been processed by the module.
In a message dated 09/02/2014 15:34:22 GMT Standard Time, time at patoka.org  


I'll be glad to check my GPS module to see what  is going on there, 
however I am still waiting for the GPS antenna to be  delivered. I tried 
to use some small form factor Trimple GPS antenna with  BC637, but 
on-board GPS module couldn't lock with it. So, my BC637 is  working in 
"freerun" mode now:

Time Settings:

Mode                     : Free Run
Time Format     : Binary
Year                     : 2014
Local Offset       : 0.0
Propagation  Delay              : 0
Current  Leap Seconds           : 0
Scheduled  Leap Event Time      : 1391731200
Scheduled Leap  Event Flag      : Insertion
GPS Time Format   : UTC Format
IEEE  Daylight Savings Flag     : Enable

I have no issues with  date stamp in that mode:

Binary Time: 02/09/2014   14:36:19.7005289   Status: 0
Binary Time: 02/09/2014   14:36:19.7105941   Status: 0
Binary Time: 02/09/2014   14:36:19.7206589   Status: 0

Even if I switch BC637 to "GPS  mode, it still using correct date. Which 
is expected, because in  accordance with documents, if GPS is not locked, 
BC637 will behave in the  same way as "free run". The difference is the 
Status. Its shows, four  bits. And one of them indicates that GPS is not 

Binary  Time: 02/09/2014  14:37:43.0045326   Status: 7
Binary Time:  02/09/2014  14:37:43.0146051   Status: 7
Binary Time:  02/09/2014  14:37:43.0246776   Status: 7

As soon as  I'll get my "bullet GPS antena" attached, I'll see what is 
going on there  for the date stamp. Also, in the documents, I saw some 
sections, which  explain how to use data registers to send some command 
to Trimble GPS.  Probably its is possible to do some corrections through 
that  procedure.
May be it is possible to attach another GPS module to the BC637  card. 
Its using 9 pin connector.
This connector is used primarily for  connecting the ACE III GPS. Data 
between the board and  the GPS receiver are via serial signals. 
Additionally, the GPS  receiver
provides a 1 PPS signal to the  board.



On 2014-02-09 06:56,  GandalfG8 at aol.com wrote:
> Oh well, full credit to Mr Trimble for  getting it right, he does bake
> exceedingly nice GPS modules and the  Ace3 doesn't have a rollover issue 
>  and it
> does report  the date correctly.
> Unfortunately, as far as I can tell  anyway, the BC637PCI takes the raw 
> time data from the  Ace3 and performs its own calculation which is where 
>  the
>  problem seems to occur, certainly it's a 1024 week issue  with the date
> from  the BC637 being displayed as June 26 1994 in  all versions of the
> associated  demo software.
> It is  possible to set the date correctly but the next packet from the 
>  GPS
> module promptly overwrites it again.
> I still  don't recall seeing this before, although with two boards  
>  behaving
> in the same fashion I'm having doubts about that, but more to  the point
> these boards indicate a firmware date of 2003 which implies  they were  
> put
> into the field like this, and that  doesn't make much sense  either.
> Any ideas anyone?, and  again has anyone else seen this and/or am I 
> missing
> something  glaringly obvious?
> Regards
> Nigel
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