[time-nuts] Re: HP Z3801A project update

[Bill Beam]

I do not know what Z3801 uses for GPS. 
I have several Motorola UT+ GPS modules running.
Older ones with V2 firmware suffer 1024 week rollover failure.
My units with V3.2 and V3.1 do 1024 week rollover correctly.
If you are able to communicate with your device using Lady Heather
she will correct any rollover error and display correct date.

On Sat, 5 Feb 2022 16:36:15 -0500, John Ackermann N8UR wrote:

>I think the problem with the Z3801 is that it expects to see specific 
>handshake things at startup, in Motorola binary protocol.  Dropping in a 
>random GPS will result in a "No GPS" error.

>John
>----

>On 2/5/22 12:44 PM, Keelan Lightfoot wrote:
>> Depending on whoG��s GPS chipset is being used, a fix might be possible. IG��ve poked around inside the firmware of a number of 
Trimble receivers (so far three generations of the 4000 series, and the Placer series). Because the first week rollover occurred in 1999, 
any receiver made close to that date already has logic to handle a week number rollover. Finding this in the disassembled code is usually 
easy because they simply add 1024 to the week number, which usually appears as an add instruction with a 0x400 immediate operand. 
changing a 0x400 to 0x800 will extend the receiverG��s lifetime another 20 years. The most difficult part of this is figuring out the 
processor used on the receiver, and figuring out how to get the patched firmware back into the receiver.
>> 
>> - Keelan
>> 
>>> On Feb 3, 2022, at 8:50 PM, Bill Beam via time-nuts <time-nuts at lists.febo.com> wrote:
>>>
>>> The date issue is a 1024 week rollover failure in the GPS receiver.
>>> A fix is to replace the GPS receiver with one that does not have this problem.
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Bill Beam
NL7F