How do I switch from NEMA to the Sirf Protocol on the ISM300?

You need to send a Carriage Return (0x0D) and Line Feed (0x0A) after the checksum (*37) for the SiRF chip to act on the message.

Ex: $PSRF100,0,57600,8,1,0*37<CR><LF>

What is the difference between the Sirf Binary and the OSP One Socket Protocol?

CSR (SirF) change the binary protocol whne they introduced the Sirf IV gps modules. The protocols are very similar but OSP has additional features.

Is you are using the ISM300x family of GPS modules use the Sirf Binary. If you are using the ISM4xx family then use OSP.

Can I flash my ISM300Fx GPS in system?

Yes, the ISM300Fx can be flashed in system by pulling pin 8 High upon power up. The module will then boot up in flash mode and you can update the firmware over the UART. This pin has a pulldown interanlly so if you do not want to flash in system you can leave this pin floating or pull to ground.

The pin is only used during initial power up.

How do I confirm my firmware revision on the GPS module?

The GPS modules do not come marked with the Firmware version. You can poll the software using Sirf Binary for the ISM300fx modules and use OSP (one Socket Protocol) for the ISM4xx version of gps modules.

If you want to run your GPS in Nema, you will need to switch to either Sirf Binary or OSP and send the module the message ID 132 – Poll Software version.

On the ISM300Fx how should I connect my antenna?

The RF in port on the ISM300 connects to the antenna (via the U.fl) or pad 1 and the input of the GPS. It is important to add the external LC circuit shown in the reference schematic on the specification because this will prevent the loss of GPS signal going into your power supply. One part we have used is the inductor L3 (33 nH is 0603HP-33NXGLW)

I need a 3 v or 5 v GPS module?

Use the ISM300f2-x family of GPS’s.

What application do you have to help troubleshoot the GPS design?

Ideally, if you can connect your PC to the UART for any of the ISM300x or ISM400x GPS modules you can run the Sirf Live. Sirf Live will show you all the satellites and C/no and allow you to send commands and become familiar with the GPS.

Simply contact for a free copy of the software.

Does the Sirf IV GPS modules have FCC/CE?

The FCC does not require that the GPS receiver has FCC or CE. We did perform FCC on the Sirf III for a specific customer request, however it is not required.

Does the ISM300x store Ephemeris data automatically?

Yes, if you use the battery back up feature and keep power alive the unit will store the data and provide warm starts. The ISM400x GPS do not require the battery back up.