13

4928C–GPS–06/06

ATR0635

3.3.2

Sensitivity Settings

For all GPS receivers the sensitivity depends on the integration time of the GPS signals. There-

fore there is a trade-off between sensitivity and the time to detect the GPS signal (Time to first

fix). The three modes, “Fast Acquisition”, “Normal” and “High Sensitivity”, have a fixed integra-

tion time. The “Normal” mode, recommended for the most applications, is a trade off between

the sensitivity and TTFF. The “Fast Acquisition” mode is optimized for fast acquisition, at the

cost of a lower sensitivity. The “High Sensitivity” mode is optimized for higher sensitivity, at the

cost of longer TTFF. The “Auto” mode adjusts the integration time (sensitivity) automatically

according to the measured signal levels. That means the receiver with this setting has a fast

TTFF at strong signals, a high sensitivity to acquire weak signals but some times at medium sig-

nal level a higher TTFF as the “Normal” mode. These sensitivity settings affect only the startup

performance not the tracking performance.

3.4

Serial I/O Configuration

The ATR0635 features a two-stage I/O-message and protocol-selection procedure for the two

available serial ports. At the first stage, a certain protocol can be enabled or disabled for a given

USART port or the USB port. Selectable protocols are RTCM, NMEA and UBX. At the second

stage, messages can be enabled or disabled for each enabled protocol on each port. In all con-

figurations described below, all protocols are enabled on all ports, but output messages are

enabled in a way that ports appear to communicate at only one protocol. However, each port will

accept any input message in any of the three implemented protocols

Table 3-5.

GPS Sensitivity Settings

GPSMODE3

(Fixed PU)

GPSMODE2

(Reset = PU) Description

0

Auto mode (Default ROM value)

Fast mode

0

Normal mode

High sensitivity

Notes:

1. Increased back-up current

2. Leave open

Table 3-6.

Serial I/O Configuration

GPSMODE12

(Reset = PU)

GPSMODE6

(Reset = PU)

GPSMODE5

(Reset = PD)

USART1/USB

(Output Protocol/

Baud Rate (kBaud))

USART2

(Output Protocol/

00

UBX/57.6

NMEA/19.2

High

User, Notice, Warning, Error

0

0

1

UBX/38.4

NMEA/9.6

Medium

User, Notice, Warning, Error

UBX/19.2

NMEA/4.8

Low

User, Notice, Warning, Error

1

–/Auto–/AutoOff

None

NMEA/19.2

UBX/57.6

High

User, Notice, Warning, Error

0

1

NMEA/4.8

UBX/19.2

Low

User, Notice, Warning, Error

NMEA/9.6

UBX/38.4

Medium

User, Notice, Warning, Error

1

UBX/115.2

NMEA/19.2

Debug

All

Notes:

1. See Table 3-7 to Table 3-10 on page 14, the messages are described in the ANTARIS4 protocol specification

2. Leave open