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NAVSYNC CW25 User Manual
Also see for CW25: User manual
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CW25 Software User Manual Page 16 of 50 Rev 03 Date: 06/16/08Copyright ©2007 NavSync Ltd.All Rights Reserved Specifications subject to change without notice.7. Power ManagementThe CW25 GPS receiver is a low power module consuming less than 0.6W typically for a 1Hz update of position. The re-ceiver contains software to dynamically reduce power consumption wherever possible. Where channels and taps are notneeded they are switched off. When the processor is not required it is put into a halt until interrupt state and the chipsclock system is geared down to reduce power consumption. All of these things are performed automatically without anyuser configuration. If further power saving is required the receiver can be reprogrammed with smaller GPS configurationsthereby permanently switching off portions of the GPS hardware and allowing the processor speed to be reduced, therebysaving power.7.1 Coma ModeFor powered battery application, which needs to reduce the power consumption, it is possible to switch the receiver intoComa mode. This configures the RF front end into sleep mode, switches off internal peripherals and places the processorin a sleep state waiting for an interrupt.Coma mode is initiated through the COMA serial command, details of which can be found in section 8.3.7.Care must be taken in the implementation of the CW25 to ensure power consumption is minimized. All input pins with-out bias resistors have potential to float mid rail and consume power during coma mode. Three GPIO pins default as inputsand do not have bias resistors. GPIO [1]/TIME_SYNC can be factory programmed to provide either an additional PPS out-put or a time synchronization input to the GPS engine. GPIO [2]/NEXT_INT can provide an interrupt event from an activelow external input. GPIO [3]/FREQ_IN provide a frequency counter input. Care must be taken to ensure that the pins haveexternal bias resistors off board to ensure they are not left floating. It is recommended that all unterminated test, Controland I/O ports are pulled high or low as appropriate (making note of the active state of some ports e.g. BSEL), with typically100k ohms.6. Operating Modes6.1 Stand Alone OperationFor stand alone operation the receiver will perform cold starts with no prior knowledge of position or GPS satellite datasuch as almanacs and ephemeris provided the antenna has a clear view of the sky to provide signal strengths of 35dB orhigher. The receiver should be allowed to track satellites for a minimum period of 15 minutes to ensure all almanac infor-mation has been received. The GPS data is stored in the EEPROM memory fitted to the CW25. Once the receiver hasbeen initialised and has current almanac and ephemeris data it may then be taken indoors for test with low level signals.Hot starts (current ephemeris data held in EEPROM) can be performed with low level signals (indoors).6.2 Network Assist OperationFor network assist operation the Navsync Network Assistance Base Station must be connected to an external antenna andbe tracking all satellites in view. The network assistance data connection is provided by an RS232 link between port 3 onthe network assistance base station and port 3 on the CW25.With the network assistance base station connected the development system can be started in indoor or outdoor envi-ronments.For more information on the Network Assistance data format please refer to section 8.4. |
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