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[another-dave]

as stated in the article at this link:
http://jarduino.com/2009/08/connect-br-355-gps/

[GS_TECH01]

I will forward your issue to our engineers, so they can better provide you with accurate information.

[GS_TECH01]

According to our engineers, the serial logic in/out of the BR355 is not inverted.

Perhaps, the problem came from the wrong setting on the logic analyzer. Since the BR355 has RS232 voltage level, the logic analyzer needs to be switched to RS232 mode instead of UART mode.

[another-dave]

Thanks for the reply. In the article referenced, it took the inversion of the logic levels into the microcontroller for the data stream to be recognized by it; so it can't have been a logic analyzer setup problem. True RS232 is bipolar with a minimum of +/- 8 volts, are you stating that the logic of the BR-355 goes below zero volts, to -8 volts or more?

[GS_TECH01]

Your issue has been forwarded to our engineers. I'll inform you once I got their response.

[GS_TECH01]

Based on our engineers, the figure below is a standard RS-232 signal map and the actual use of BR-355 measured in the oscilloscope signal.

It is in line with RS-232 specification and there is no "reverse" problem.

In the RS-232 signal, the negative voltage = logic '1 ' and the positive voltage = logic '0'.

The UART signals is 0V = logic '0 ' and positive voltage = logic '1'.





Let me know if you have any questions.

[another-dave]

Thank-you, this explains why the author of the article could use a TTL inverter to get valid data. Hope he clamped the signal to ground thru a diode to clip those negative swings.

[ByteMan]

Dear All,
I'm new of this forum, recently I've purchased the BR-355 (PS2) then with the serial in interface option.
Now I've to interface this GPS receiver with a custom designed board equipped with a PIC microcontroller.
I've two question, one about the serial interface and one about the GPS programming.

Serial Interfacing
Regarding this stuff I've found very useful the USG_TECH10 post with the signal diagrams, from this I can understand that is a classical RS232 interface, then I can use a MAX202 to decode it into the standard 5V UART level of my microcontroller, the MAX202 perform the level inversion and the level adaptation in order to feed the right signal on the microcontroller USART port. I've read that many  people are using a inverter logic gate approach by means the 74HC04 or 74HC240. What I like to ask now is if my idea to use a simple MAX202 ic shoud be fine for my purpose. Could you let me know me your think?

GPS Programming
I'm new with this type of device, from reading around in the net I can understand that the module communicate by using the NMEA0183 protocol standard then by means ASCII string. In my think the GPS will output various type of string sequentially, but If I'm right (please confirm this or correct me) I can instruct the GPS to output only some string. From my point of view I need only the position and the UTC time because I've to store these info on a EEPROM which into the my custom board in order to have a rougly data logger. Because the GPS have also a RX input I think that this line can be used to send certain command to the GPS unit and then also to instruct the GPS to send only some string. If I'm right where I can search what is the command that I can sent to the GPS receiver in order to instruct it to output only some NMEA string? I've read that there is some proprietary sentence, where I can reterieve some document or specification to help me into the GPS configuration? Could you please help me in that sense?

Thanks in advance for your help and my best wishes for Merry Christmas!
ByteMan a.k.a. Powermos

[GS_TECH01]

For Serial Interfacing, the MAX202 could possibly work with our device. Just let us know how it goes.

As for GPS Programming, it is possible to configure the device to only output specific sentences. Since you only want the position and UTC, you need to enable the GLL (Latitude, longitude, UTC time of position fix and status) and RMC (Time, date, position, course and speed data). For more information about NMEA, refer to this document: http://www.usglobalsat.com/store/downloads/NMEA_commands.pdf

To enable the GLL and RMC on the device, follow the steps below:

1. Download and install this software: http://www.usglobalsat.com/store/downloads/SiRFDemo387.zip
2. Open up the Sirf Demo software.
3. Connect your device, choose the correct COM port, and select the 4800 baud rate.
4. Go to Action > Open Data Source.
5. Next, go to Action > Switch to SiRF Protocol.
6. Then, go to Action > Switch to NMEA Protocol.
7. In the NMEA Setup window, select 1 for GLL and RMC and set the rest to 0.
8. Choose the 4800 baud rate under the Baud Rate and click Send.
9. In the Debug View - NMEA window, you will only see the GLL and RMC sentences.

You can test out the device with our GPSInfo Utility (http://www.usglobalsat.com/store/download/62/vista_32bit_gps_info_utility.zip) to see if it's working properly.

Note: Be sure not to click on anything else in this software, as you can render your device unusable. Moreover, the device will return to its default settings once the internal battery drains when it is removed from power.