GPS Date wrong by 20 years

Information about using GPS units with motec devices

GPS Date wrong by 20 years

Postby AFK88L on Fri May 15, 2026 1:19 pm

I recently noticed an issue with my C127 dash display showing the wrong date.

I believe I've worked out the root cause (and a workaround), but just wondering if a firmware update is possible that could fix this issue?

It's been working correctly for years, but some time in the past 6-12 months (hadn't been paying that much attention) the date started to display incorrectly.

Setup is a C127 Race Display Kit that I purchased back in Aug 2016. This came with a 10Hz GPS unit (L10).

I've been using my own custom Display Creator design, with no changes since 2021, and it had always been correct until now. I output the DOW Day/Month and Time (24hr) to the bottom section of the display, as below.

Image

This was taken on "Tue 28/04" but the display was showing "Tue 12/09".

Thinking a Display Creator issue, the next day I updated the display to output the full date (also upgraded to Dash Manager 6.51.12.0 and Display Creator 6.5.1.0205 at the same time to see if there was a fix already).

Image

So the full date showed as 13/09/2006 instead of 29/04/2026.

I finally realised I should actually monitor the GPS Date channel value and found that's where the issue is. The GPS unit is outputting the wrong date?

Image

It was outputting a value of 130906 (DDMMYY).

I noticed something when I did a date calc between the two dates.

Image

1024 weeks looked suspect.

I have since learned GPS systems use a week count plus time-of-week value, since a certain date.

So it looks like my L10 GPS device might only be using a 10-bit value for the weeks (max value 1023) which means there's a date rollover issue every 1024 weeks (since some internal hardcoded start date), I think?

My workaround has been to create a constant channel with a value of 7168 and use this as the "Date Offset (Days)" in the Real Time Clock config of Dash Manager.

That works, but wondering if a firmware update is possible to ensure the GPS Date channel value is correct in the first place?
AFK88L
 
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Re: GPS Date wrong by 20 years

Postby Stephen Dean on Mon May 18, 2026 6:33 pm

Hi,

Try this resolution.
Stephen Dean
MoTeC Research Centre Melbourne, Australia
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Stephen Dean
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