[time-nuts] Rapco 1804M - serial problems?

mike cook michael.cook at sfr.fr
Sun Oct 16 13:15:31 EDT 2011


Le 16/10/2011 18:34, David J Taylor a écrit :
> I've just got a Rapco 1804M and while it works, within the limits of 
> my antenna placement, the RS-232 serial out doesn't read very well, 
> and seems to have incorrect characters.  The voltage levels look OK, 
> and the terminal emulation program is set to 4800 baud, 8-bit, no 
> parity, one stop bit, no flow control.  I've tried other 
> combinations.  As near as I can measure, the baud rate is 4800.
>
> Here's some sample output:
>
> _____________________________________________
> UTC Time  : 16:65:19 16/10?1q
> UTC Time  : 16:25:20 16/10/11
>
> Position  : 53 54.406 N  002 12.075 W  0239 M
> PDOP      : 02
> Sat PRN   : 28,19,32,01,11<22
> Sat levål : 00,12,13,06,05,03
> Fix, Mode : 2D , Coarse
>
> UTC Time  : 16:25:21 16/10/11
> UTC Time  : 16:25:22 16/10/11
> UTC Time  : 16:25:23 16/10?11
> UTC Time  : 16:25:24 16/10/11=
>                              UTC Ti}e  : 16:25:25 16/10?11
> UTC Time  : 16:25:26 16/10?11
> _____________________________________________
>
>
The data is nearly all good, so probably not a rs232 rate issue. Looking 
at the transformations in the above data,
/ => ?
1 =>q
, => <
CR => =
m => }

they are all single/multiple bit flips in the top nibble of the 
character hex value. Maybe it's a UART that has hickups.
I couldn't find a schematic, but may be worth looking to see what's 
connected to the RS232 tranceiver chip..


> The same serial port works correctly with 9600 baud Garmin signal, and 
> I don't have any other available computers with spare RS-232 ports I 
> can test against.
>
> Am I missing the obvious, or is there something wrong with the serial 
> port?  I do appreciate that the serial port isn't critical to the 
> correct operation of the 1804M, but this has cast doubts about this 
> particular unit into my mind!
>
> Thanks,
> David GM8ARV




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