Trimble Outdoors SK8 - Manual (Page 40)

2-4 Lassen-SK8 Embedded GPS Module
Hardware Integration
The receiver does not require any special power up or down sequencing. The receiver
power is supplied through pin 2 of the I/O connector. Refer to Table 2-2 for the +5 VDC
power specifications.
The Lassen-SK8 module provides an input for battery back-up (BBU) power to keep the
module's RAM memory alive and to power the real-time clock when the receiver's prime
power is turned off. RAM memory is used to store the GPS almanac, ephemeris, and last
position. User configuration data, including port parameters and receiver processing
options, are stored in non-volatile EEROM which does not require back-up power. By
using battery back-up, time to first fix is reduced to 20 seconds (typical). Though not
required, providing BBU power can reduce power-on time. A 3.6 volt lithium battery used
for back-up power can last up to five years.
*
Note – 3.2V is the minimum allowable voltage. When the power output drops below 3.2V,
the real-time clock may not operate over the specified full temperature range.
The Lassen-SK8 receiver module will maintain full performance specification when the
prime power line is coupled with less than 100 mV of ripple noise, peak to peak from 1Hz
to 1MHz.
*
Note – The Lassen-SK8 Starter Kit motherboard contains a 3.6V lithium battery.
2.4 Serial Interface
As an embedded design, the Lassen-SK8 receiver module provides direct CMOS
compatible TTL level serial I/O. The RX and TX signals on the J4 I/O connector are
driven directly by the DUART on the Lassen-SK8. Interfacing these signals directly to a
DUART in your application circuitry provides direct serial communication without the
complication of RS-232 or RS-422 line drivers.
*
Note – The serial I/O signals on J4 are TTL level. They are not inverted or driven to RS-
232 levels.
Table 2-2. Power Requirements
Signal Voltage Current J4 Pin
VCC +4.75 to +5.25 200 mA 2
Battery Backup +3.2 to +5.25 0uA with prime power; 2uA
@ 3.5V, 25°C without prime
power 4
Ground 0 - 8