At outdoor signal levels the time taken to obtain a ‘hot’ position fix is under 2 seconds. With a size of just over an inch square (25 x 27 mm) the CW25 is specifically designed to be integrated with communi- cations devices such as GSM, CDMA, UMTS modems or any other communications medium.
1.3 GPS positioning and navigation The CW25 Receiver needs to be able to see at least 4 satellite vehicles (SV’s) to obtain an accurate 3-D position fix. When travelling in a valley or built-up area, or under heavy tree cover, you will experience difficulty acquiring and maintaining a coherent satellite lock.
CEP and SEP are not affected by large errors, which could make the values an overly optimistic measurement. These probability statistics are not suitable for use in a high accuracy positioning system. The CW25 reports all accuracy’s in the form of a standard deviation (RMS) value.
30ns rms accuracy, <5ns resolution, Factory customisable pulse width Event Input 30ns rms accuracy, <10ns resolution Frequency Output (GPIO [0]) 0 MHz to 20 MHz (CW25-NAV) 10 Hz to 30 MHz (CW25-TIM) Receiver Type 12 parallel channel x 32 taps up to 32 point FFT. Channels, taps and FFT can be switched off to minimize power or simulate simpler designs.
3.1 Physical Interface Details The interface to the CW25 is via 1mm castellation on a 2mm pitch. There are 42 connections in all. There is also an RF connector for connecting to the GPS antenna. The details of the interface connections are given below.
RF_IN castellation. If the RF_IN castellation is to be used, the pad should be shortened by 0.5mm underneath the CW25 and standard RF design practices must be observed.
4. SIGNAL DESCRIPTION The signals on the CW25 are described in the table below. All Test, Control and I/O ports are CMOS 3.3V compatible un- less specified otherwise. 4.1 Power Signals RF_3V3 Type: Power Direction: Input Pin: 19 The RF supply input. This 3.3V ± 10% input supplies the 3.0V LDO regulator in the RF section of the CW25.
This signal has an RF blocked connection to the ANT_SUPPLY signal. This is the same signal presented on the RF connector on the CW25. Only one antenna connection should be made. If the RF connector is to be used, then there should be no connection, even an unconnected pad, to this castellation.
The Power On Reset signal. This active low, open collector signal is the master reset for the CW25. This should be driven with an open collector reset circuit for a minimum of 100ms. An external pull-up is not required if the 100K internal pull-up is sufficient. The CW25 can be held in reset by asserting this signal.
DIG_GND. N2WCK Type: I/O Direction: Input/Output Pin: 28 The NavSync 2 Wire Clock signal. This is the open collector I C compatible clock signal for the 2 wire serial interface. The signal return path is DIG_GND. N2WDA Type: I/O...
The power on reset for the CW25 is generated on-board by the regulator in the RF section from the RF_3V3 signal. The RF_3V3 signal must be applied to the CW25 at the same time as the DIG_3V3, if the on-board power on reset is to be used.
7. Power Management The 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 not needed they are switched off.
All ports are configured as 8, bits no Parity, with no handshaking. 8.2 Output Format There are two types of messages that can be output from the CW25 receiver, these are split into NMEA sentences and Debug messages. Both types of outputs are ASCII strings.
8.2.1.8 POLYT - Time of Day $POLYT,hhmmss.sss,ddmmyy, UTC_TOW ,week, GPS_TOW ,Clk_B , Clk_D ,PG,LocalTTag,BAcc,TAcc,BLANK*cs Name Description $POLYT Navsync Proprietary NMEA sentence header (Position Data) hhmmss.sss UTC Time in hours, minutes, seconds and decimal seconds format. ddmmyy Date in day, month, year format.
$POLYP,hhmmss.sss,Latitude,N,Longitude,E, AltRef ,FS,Hacc,Vacc, SOG , COG , V_vel,ageC,HDOP,VDOP,PDOP,GDOP,TDOP,GU,RU,DR*cs Name Description $POLYP Navsync Proprietary NMEA sentence header (Position Data) hhmmss.sss UTC Time in hours, minutes, seconds and decimal seconds format. Latitude User datum latitude degrees, minutes, decimal minutes format (ddmm.mmmmmm) Hemisphere: ‘N’= North, ‘S’ = South Longitude User datum longitude degrees, minutes, decimal minutes format (dddmm.mmmmmm)
Note: {} designate optional sections that appear only if there is satellite data Name Description $POLYS Navsync Proprietary NMEA sentence header (Satellite Data) Number of GPS satellites tracked Satellite PRN number (1-32) Satellite status - = not used U = used in solution...
Any additional pages specific to soft- ware versions are not described in this manual. 8.2.3.1 Navigation and Timing Summary ($11) Navigation Summary Page 12x32x32x16 CW25 1.741 May 10 2004 15:03:41 Time 140533.70 3840 1270 137133.708 1...
Q: Command, a query command to the CW25 receiver. S: Command, requires the CW25 receiver to set system settings. R: Response to a CW25 receiver, response to a $PRTH Query or an acknowledgement of a $PRTH Set. <id> is a 4 character command identifier.
= Drone, Missile dynamics (<16g) = Pure least squares mode (ie semi-infinite dynamics assumed) Default for CW25-NAV is 3, maximum is 5. Default for CW25-TIM is 1 and changes to 0 after 10 minute location survey completed, maximum is 5.
The data areas that can be cleared include satellite almanacs, ephemerides, network assist and receiver configuration parameters. Note that “sleep” mode is not currently supported in the CW25 technology. This command invokes a 2 second time-out prior to the reset being called.
Explanation of Parameters Frequency The frequency in Megahertz that the receiver will output. CW25-TIM defaults to 10 MHz, 30 MHz maximum. CW25-NAV defaults to 0 MHz (disabled), 20 MHz maximum. e.g. for 10kHz = 0.010 = switch digital frequency off.
(epochs). The dead reckoning will progress at constant velocity for the first half of this period and then reduce to a standstill during the second half. Note that since this value has units of epochs, it will have a different effect on a 1Hz CW25 receiver to that on a 2Hz, 5Hz or 10Hz CW25 receivers.
8.4 Network Assistance Input The CW25 uses network assistance data to allow acquisition and tracking of GPS satellites in low signal levels. The net- work assistance data is base on the TIA/EIA/IS-801 specification as using the CDMA network. The format used is an ASCII version of the data to allow the contents of the messages to be displayed on a terminal.
$PRTHS, U3CM 9.1 NMEA Configuration Query ($PRTHQ, UxOP): The command takes the form “$PRTHQ,UxOP” where x is a port number. On the CW25 platform, the port number is always between 1 and 3 inclusive. The remainder of the strings is of the form “$PRTHR,UxOP,GLL=1,GSV=4,PLT=1” where x is the port number for which the information was requested.
CW25 platform. Consequently, the Rx and Tx baud rates must always be specified to be the same value. In addition, the CW25 platform does not currently support the use of parity, or of stop bit settings other than 1 stop bit. The supported baud rates are: 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200, and 230400.
Navsync Base Station. These messages are suitable for use as a Network Assistance input to the CW25 receiver module. They are a series of ASCII comma separated messages which are output from UART3 of the CW25 based ILD Base Station Receiver at 38400,8,N, 1.
< 0.33 v at 6mA sink) 13. Frequency Output The CW25 is capable of producing a user select frequency. The frequency is output on GPIO [0] port (pin 39). The frequency is configured using the FRQD command as detailed in section 8.3.10.
1.8V source e.g. switch mode power supply, rather than the on-board linear regulator. If the source impedance of the power supply to the CW25 is high due to long tracks, filtering or other causes, local decoupling of the supply signals may be necessary. Care should be taken to ensure that the maximum supply ripple at the pins of the CW25 is 50mV peak to peak.
14.4 Battery Backup The CW25 has an on-board real time clock (RTC). This is used to store date and time information whilst the CW25 is pow- ered down. Having a valid date and time speeds the time to first fix (TTFF), allowing the CW25 to meet its quoted TTFF specification.
14.6 Reset Generation The power on reset for the CW25 is generated on-board. It is generated by the regulator for the RF section. This signal is an active low, open collector signal and is presented on the NPOR castellation. If it is desired to extend the power on reset signal or provide a manual reset for the CW25, this signal can be driven from an open collector source at any time.
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CW25 User Manual Revision Revision Date Notes P 0.1 01/24/07 Preliminary User Manual P 0.2 05/03/07 Updated to new Format V1.0 08/26/07 Updated to Released Version V1.03 11/07/07 Revisions and Edits Update 04/21/08 Data Updates & Update to new Revision System 06/16/08 Data Revisions to Section 8 &...