28509 Datasheet 28509 | P4-P6

$GPTXT,01,01,02,LLC FFFFFFFF-FFFFFFED-FFFFFFFF-FFFFFFFF-FFFFFF79*21

$GPTXT,01,01,02,ANTSTATUS=INIT*25

$GPTXT,01,01,02,ANTSTATUS=OK*3B

This is a set of initial empty NMEA sentences before a fix has been established, just after the module has

been powered on:

$GPRMC,,V,,,,,,,,,,N*53

$GPVTG,,,,,,,,,N*30

$GPGGA,,,,,,0,00,99.99,,,,,,*48

$GPGSA,A,1,,,,,,,,,,,,,99.99,99.99,99.99*30

$GPGLL,,,,,,V,N*64

A valid position fix will have NMEA sentences that look something like this:

$GPRMC,041845.00,A,3846.50323,N,12115.39233,W,0.264,,040814,,,A*67

$GPVTG,,T,,M,0.264,N,0.488,K,A*27

$GPGGA,041845.00,3846.50323,N,12115.39233,W,1,03,7.16,72.5,M,-26.8,M,,*50

$GPGSA,A,2,18,21,15,,,,,,,,,,7.23,7.16,1.00*0A

$GPGSV,4,1,14,14,18,184,,15,33,055,15,16,19,263,,18,78,009,28*75

$GPGSV,4,2,14,19,11,320,,21,68,067,29,22,53,256,,24,05,105,*74

$GPGSV,4,3,14,26,05,033,,27,38,308,14,29,17,156,09,46,36,147,*79

$GPGSV,4,4,14,48,43,198,,51,43,158,*78

$GPGLL,3846.50323,N,12115.39233,W,041845.00,A,A*77

Your application can parse these sentences for GPS fix information as needed. Parallax provides some

sample programs that parse these NMEA sentences and makes the data available to your application.

See the Resources and Downloads section for more information. For more information about NMEA

sentences and what information is contained in the fields, check out this website:

http://www.gpsinformation.org/dale/nmea.htm

Update Rate

By default, the most up-to-date GPS fix information is transmitted from the module at a rate of 1 Hz, that

is, once per second. This rate can be increased up to 10 Hz; see the manufacturer’s datasheet for more

information.

Navigation Mode

There are two navigation modes, continuous navigation and static hold. In the default continuous

navigation mode, the PAM-7Q module uses its position acquisition system to constantly download

updated almanac information and track satellites. With this information, the module transmits the most

up-to-date fix information to your connected device. Continuous navigation mode is enabled by default

so your application will receive constant fix updates, regardless of the speed or distance traveled. When

the module is stationary, you may see very minute changes in reported speed.

Atmospheric anomalies cause the precise timing signals received by the module to drift ever so slightly,

causing the module’s reported location to minimally vary. Tall buildings, trees, and overhead

obstructions also contribute to slight shifts in timing measurements from the satellites. Static Hold mode

is used to filter out this “noise” while the module is not in motion. Thus, the module will not report

position changes unless it has moved several meters. This feature is commonly used in automobile GPS

navigation systems.

Time Pulse and Satellite Lock LED

The Time Pulse pin on the PAM-7Q GPS module outputs a pulse that is synchronized with the GPS

device’s “epoch.” By default, the PAM-7Q GPS device’s epoch is set to a 1 second period and it is

synchronized with the time base received from the network of GPS satellites in orbit. By default, this

active high pulse has a 10% duty cycle, or 100 ms. The time pulse is only active at the top of each

second and only occurs once the module has acquired a GPS satellite lock. If your application requires it,

this signal can serve as an interrupt request.

The blue satellite lock LED on the underside of the module also makes use of this time pulse signal to

give you a visual indication of when the GPS module has locked onto a GPS signal. This LED also doubles

as a power indicator to the module. As soon as power is applied, the LED will light indicating the

presence of power. Once at least one satellite is being tracked, the LED will begin to blink with the

module’s time pulse.

Communication Protocol

The PAM-7Q GPS Module supports multiple physical communication protocols. The module was designed

to communicate primarily through a TTL UART – with the TXD transmit pin and RXD receive pin. This

UART operates at a default baud rate of 9,600 bits per second (BPS), eight data bits, one start bit, one

stop bit, and no parity (8N1). However, the baud rate and character framing settings can be changed to

other standard configurations, up to a maximum of 115,200 baud. If 10 Hz navigation update is

required, it is recommended that you change the module’s baud rate to a higher setting. This is because

at 9,600 baud, there is not enough time to send a full set of NMEA sentences in a 100 ms period.

For convenience, advanced users can take advantage of the optional I

C slave port. As you would

expect, this communication will take place on the SCL and SDA pins. Note that the pins have not been

populated – this is to prevent damage to the module as the signals are not pre-conditioned. See the

Precautions section below for more information.

The PAM-7Q GPS module also supports multiple structured data protocols. By default, the module is set

to output NMEA sentences automatically. The module will also respond to other data protocols. uBlox

has created two proprietary protocols called PUBX and UBX. The PUBX protocol is similar to the NMEA

protocol in that data is communicated in ASCII format. For more compact data transmissions, the UBX

protocol exchanges data in a binary format. Most users will not need to configure the module with these

protocols, but it is good to be aware of their existence.

Additional information about how to communicate with the module via these special protocols or with I

can be found in uBlox’s “Receiver Description Protocol Specification” document.

Other Features and Precautions

Battery Backup Aided Start Feature

The module is designed with a 30 mF super-cap that acts as a rechargeable battery backup. This allows

the GPS module to retain almanac data for more than 30 minutes which aids in quicker Time To Fix

(TTF). With this aided start, the module can acquire a valid location fix in as little as 5 seconds.

SCL and SDA Line Precautions

Communication with the PAM-7Q GPS module is intended to happen via the TXD and RXD lines. For

advanced users, I

C communication signals are provided as an option. However, there is no signal

conditioning present on these lines. Only signal the SCL and SDA lines at 3.3 V. Additionally, the I

lines are not externally pulled up. If you do decide to communicate via I

C, make sure that the SDA and

SCL lines are pulled up to 3.3 V in order to comply with the I

C standard.

Handling Precautions

When handling the PAM-7Q GPS module, handle the module from the edges only. Take special care not

to put undue pressure on the GPS antenna from the top-side of the module. As part of the

manufacturing process, we have applied epoxy to the GPS antenna to make the module resistant to

stress, but excess force could still damage the module.

Module Dimensions

Pin spacing is standard 0.1” for a breadboard friendly design. Mounting holes are spaced by 1.25” and

0.75” center-to-center, with a .125” diameter, and accepts #4-40 screws.

Resources and Downloads

Check for example programs on Parallax’s PAM-7Q product page. Just search for the product

number: 28509. Additionally, uBlox publishes detailed datasheets and other technical descriptions on

their website. If you want to gain full use of all of the GPS receiver’s special features, take a look at

uBlox’s “Receiver Description Protocol Specification” document. This document is very complete and

describes every setting of the PAM-7Q module you can change, as well as the communication protocols

the module supports.

P1-P3 P4-P6

28509

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Parallax

Description:

GPS Modules PAM-7Q GPS Module

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