User`s guide

Chapter 3 - Receiver Descriptions

Operating Without a Backup Source

Without any backup power none of the setup information mentioned above is available to the

receiver upon restart. The receiver must now perform a “Cold Start”, where position, time, and

almanac information are not available. Note that this is not a serious problem, but Time To First

Fix (TTFF) will be somewhat longer than if the information had been available.

The main thing the system designer must keep in mind is that a receiver coming up in a Cold

Start scenario is defaulted to Motorola Binary protocol, and NO MESSAGES are ACTIVE. The

receiver is running through its normal housekeeping routines, developing new fix data, etc., but it

will not send any of this data out of the serial port until it is requested.

If the receiver is being used as part of a larger system where the user has access to the

receiver’s serial port through application software such as WinOncore12, the user can simply use

the software to reinitialize the receiver into the desired mode.

Embedded developers have to be careful since they typically do not have direct access to the

receiver’s serial port. In this case the best thing to do is to ASSUME that the receiver will always

wake up in a defaulted condition and include code in the application software to initialize the

receiver every time power is cycled. This code may be as simple as merely directing the receiver

to output a standard Motorola binary Position/Status/Data message (@@Ha for instance), or may

possibly involve uploading a stored almanac, switching the receiver over to NMEA mode and

initializing the desired NMEA strings. No matter, the effect is still the same: if the receiver wakes

up with all setup information intact, there’s no harm done, the initialization commands merely

reinforce the configuration data already present in RAM. If the receiver powers up in the defaulted

mode the initialization code ensures that the receiver operates in the manner intended.

NOTE: Receivers fitted with onboard batteries CANNOT

utilize external backup power.

Although there are many reasons for not using a receiver fitted with a battery, the three instances

that come up most often are:

1. Remote systems that are expected to run unattended for long periods of time. The

most common example of this type of situation is in the timing receivers used to keep

CDMA cell sites synchronized. These systems are expected to operate for 10-20

years in remote areas and having to replace batteries every 5 years or so would

present a severe maintenance problem.

2. Operation in continuous high temperatures. Although M12+ receiver is rated for

operation at +85

C, the lithium cells have a service ceiling of +60

3. Operation at low duty cycles. A common example of this type of application is

oceanographic buoys. These might typically turn on the M12+ once a day for a few

minutes, get a fix, and then power the receiver back down. Over time the result is that

the battery is never allowed to charge up between power cycles and slowly

discharges. A better choice in this situation is to use an external primary battery with

sufficient capacity for the entire deployment, or use of a “SuperCap” or

“UltraCapacitor” as a backup power source. Since these can be charged up in a

matter of seconds while the receiver is getting it’s daily position fix, loss of capacity

over time is not an issue.

Motorola GPS Products - M12+ User's Guide Revision 6.X 09FEB05