VPN1513 GPS Receiver Module documentation problems
macegr
Posts: 5
Couple of issues with the VPN1513 board (Parallax 28506).
1.) Serial interface is 3.3V, not 5V. Interface voltage isn't documented. This voltage change can cause problems when connected to some devices, which expect higher minimum HIGH logic levels. In my customer's case, an earlier (discontinued) Parallax 5V TTL GPS module worked perfectly but this new module did not. An external level conversion circuit will need to be constructed. Documentation needs to be clear this is a 3.3V interface. It may work correctly in the exact example configuration provided, but may be unreliable or cause damage if used by someone assuming it's a 5V interface.
2.) In RAW (NMEA 0183) mode, the serial baud rate is actually 4800. The documentation only ever mentions the new interface speed of 9600, which I imagine holds true for the SMART mode of operation. This significantly increased the time required to troubleshoot the previous voltage level issue, because there were actually two problems to solve before communication with the GPS module was possible. Documentation needs to explain that baud rate changes to 4800 in RAW mode, or else the firmware needs to be updated to 9600 baud if this was an error.
Hope this helps anyone else having problems with this module.
1.) Serial interface is 3.3V, not 5V. Interface voltage isn't documented. This voltage change can cause problems when connected to some devices, which expect higher minimum HIGH logic levels. In my customer's case, an earlier (discontinued) Parallax 5V TTL GPS module worked perfectly but this new module did not. An external level conversion circuit will need to be constructed. Documentation needs to be clear this is a 3.3V interface. It may work correctly in the exact example configuration provided, but may be unreliable or cause damage if used by someone assuming it's a 5V interface.
2.) In RAW (NMEA 0183) mode, the serial baud rate is actually 4800. The documentation only ever mentions the new interface speed of 9600, which I imagine holds true for the SMART mode of operation. This significantly increased the time required to troubleshoot the previous voltage level issue, because there were actually two problems to solve before communication with the GPS module was possible. Documentation needs to explain that baud rate changes to 4800 in RAW mode, or else the firmware needs to be updated to 9600 baud if this was an error.
Hope this helps anyone else having problems with this module.
Comments
Thanks for pointing this out, we'll get the documentation updated ASAP.
Cheers,
Jessica
Rick Murray
The firmware is available on the bottom right of this page (Under Open Source Downloads):
http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/28506/List/0/SortField/4/ProductID/757/Default.aspx
If you go to page one of this document, you will see four holes on the right side to accept a PropPlug. Yes , that is JP1. That is for re-programming the Propeller's EPROM. You can't retrieve the program from the EEPROM, but the program loaded is the program in the firmware listing.
EDIT: Posted while Ray was replying. (Never been a fast typist)
-Tor
I am using the Propeller education kit with plans to go to USB board.
Command is hard-coded, output is to CRT
A couple of thing came up:
1. As is published, 9600 baud is the correct rate.
2. Normal mode (not inverted) is correct polarity.
3. The command set is prefaced with "!GPS", got that from Stamp demo. Spent several hours with scope trying to figure that one out.
4. The 1513 doesn't pull the SIO line all the way to 0 (.4v or so) but does work. (tried pull-down of 10K) Perhaps a pin release issue??
5. Do only the number of reads that you expect bytes of data; too many; locks and waits.
6. Documention error (??) GetDate returns UTC Date in Day, Month,Year format
Rick Murray