MCS38140PG05C

2

MOTOROLA

1.0 Summary

The RoadRunner Application Specific Integrated Circuit

(ASIC) represents the 5th generation of Global Positioning

System (GPS) digital signal processing integrated circuits

used in Motorola commercial GPS products. When com-

bined with an RF down converter, microprocessor, and

application software, it can become the heart of a broad line

of high performance and low cost GPS sensors. The

RoadRunner ASIC provides additional features and

achieves higher levels of performance at the same time

being a driver for the design of low cost GPS applications.

The RoadRunner ASIC contains circuitry to simultaneous-

ly track up to eight satellites. Each independent receiver

channel within the ASIC can be commanded to acquire and

continuously track a single spread spectrum signal using any

of the GPS gold codes or the FAA WAASS PN codes. The

ASIC performs the following major functions of a GPS

receiver:

• Samples the down converted IF signal with a 1 bit A/D

converter

• Down converts the signal to baseband by removal of the IF

the carrier frequency

• Signal de–spread with a replica PN code

• Doppler wipe off

• Provides digital in–phase and quadrature PROMPT and

EARLY–minus–LATE outputs

The microprocessor and software control each receiver

channel independently, and step the channel through the

satellite acquisition process until continuous track is

achieved. The acquisition and tracking functions are com-

pletely controlled by software, allowing for maximum flexibil-

ity for system enhancement and integration while

maintaining a cost effective implementation.

Digital signal processing software running in the micropro-

cessor controls the satellite tracking function by closing both

code and phase/frequency tracking loops and converting the

ASIC outputs into pseudorange and pseudorange–rate

measurements, and decodes and stores the satellite broad-

cast ephemeris and clock correction data for use in down

stream data processing software. These measurements and

data are subsequently used in the receiver’s PVT software

(position, velocity, and time) in order to translate the range

measurements and ephemeris data into user position

coordinates.

The RoadRunner’s extended features include:

• Multiple microprocessor interface support (68330, 331,

332, 68HC000, 68EC000)

• Full in–phase and quadrature outputs on PROMPT and

EARLY minus LATE correlators

• Supports FAA WAASS PN codes

• Runs from 5.0 or 3.3 Volt power supply

• On–chip Real Time Clock

• On–chip UART

• Inexpensive 68 pin package

A top level block diagram of a typical GPS receiver using

the RoadRunner ASIC is detailed in Figure 1.1. Five major

subsystems are required to complete the design of a GPS

receiver. These subsystems include an antenna/LNA, a RF

downconverter (such as the Motorola MRFIC1502), a

reference oscillator, the RoadRunner ASIC, and a micropro-

cessor/memory system. When the RoadRunner ASIC is

combined with the GT Oncore

™ system software, the GPS

receiver will receive, track, and decode data from up to 8

parallel satellites to provide high performance position,

velocity, and time data to a user application.

AND

Figure 1.1 A Typical GPS Reciever Block Diagram with a RoadRunner ASIC

PLL / VCO

A/D

8 CHANNEL

CORRELATOR

CARRIER

FLASH ROM

128K X 8

128kX16

NON–VOLATILE

RAM

32K X 8

128K X 8

REAL TIME CLOCK

32 kHz OSCILLATOR

LPF

BPF

VCO

TUNE

BPF

BPF

LNA

MRFIC1502

REF OSCL

F–IF

MPU

INTERFACE

UART

MODULE

I/O PORT

MPU

68330

68331

68332

68000

68EC000

VRAM

MPU_CLK

A(7:0), D(7:0)

PWR

CLK

GEN

TEMP

SENSOR

SPI

GPIO

GLUELESS

INTERFACE

R/W, CS, ...

1–PPS

CURRENT

SENSOR

PWM’S

VCC

SW

WIPEOFF

SAMPLE CLK

I/O

PORT