3.3 CONNECTION WIRING DESCRIPTION
The GPS 35LP features a stripped and pre-tinned cable assembly for connection flexibility. The following is a functional description of each wire in the cable assembly.
Red: Vin - Regulated +3.6V to +6V, 150 mA (maximum) in the -LVx versions. Typical operating current is 120 mA. Transients and overvoltages are protected by an internal 6.8V transient zener diode and a positive temperature coefficient thermistor. With voltages greater than 6.8Vdc the zener will draw several amps of current through the thermistor, causing it to heat rapidly and eventually power the unit off, unless an external fuse blows first. When proper supply voltages are returned, the thermistor will cool and allow the GPS 35-LVx to operate. The CMOS/TTL output buffers are powered by Vin, therefore a 3.6Vdc supply will create 3.6V logic output levels.
In the -HVx versions, Vin can be an unregulated 6.0Vdc to 40Vdc, optimized for 12Vdc. Typical operating power is 800mW This voltage drives a switching regulator with a nominal 4.4Vdc output, which powers the internal linear regulators, and the CMOS output buffers.
Black: GND - Power and Signal Ground
White: TXD1 - First Serial Asynchronous Output. CMOS/TTL output levels vary between 0V and Vin in the -LVC version. In the -LVS and -HVS versions a RS-232 compatible output driver is available. This output normally provides serial data which is formatted per “NMEA 0183, Version 2.0”. Switchable to 300, 600, 1200, 2400, 4800, 9600 or 19200 BAUD. The default BAUD is 4800.
Blue: RXD1 - First Serial Asynchronous Input. RS-232 compatible with maximum input voltage range -25 < V < 25. This input may also be directly connected to standard 3 to 5Vdc CMOS logic. The minimum low signal voltage requirement is 0.8V, and the maximum high signal voltage requirement is 2.4V. Maximum load impedance is 4.7K ohms. This input may be used to receive serial initialization / configuration data, as specified in Section 4.1.
Purple: TXD2 - Second Serial Asynchronous Output. Electrically identical to TXD1. This output provides phase data information for software version 2.03 or above. See Appendix C for details.
Green: RXD2 - Second Serial Asynchronous Input. Electrically identical to RXD1. This input may be used to receive serial differential GPS data formatted per “RTCM Recommended Standards For Differential Navstar GPS Service, Version 2.1” (see Section 4 for more details).
Gray: PPS - One-Pulse-Per-Second Output. Typical voltage rise and fall times are 300 nSec. Impedance is 250 ohms. Open circuit output voltage is 0V and Vin in the -LVx versions, and 0V and 4.4V in the -HVx. The default format is a 100 millisecond high pulse at a 1Hz rate, the pulse width is programmable from a configuration command in 20msec increments. Rising edge is synchronized to the start of each GPS second. This output will provide a nominal 700 mVp-p signal into a 50 Ohm load. The pulse time measured at the 50% voltage point will be about 50 nSec earlier with a 50 Ohm load than with no load.
Yellow: POWER DOWN - External Power Down Input. Inactive if not connected or less than 0.5V. Active if greater than 2.7V. Typical switch point is 2.0V @ 0.34 mA. Input impedance is
15K Ohms. Activation of this input powers the internal regulators off and drops the supply current below 20mA in the -LVx versions, and below 1mA in the -HVx. The computer will be reset when power is restored.
Section 4