Motorola M12 Oncore Guide de l'utilisateur télécharger pdf (Page 37)

Chapter 3 - Receiver Descriptions

System Integration

The M12+ receiver is an intelligent GPS sensor intended to be used as a component in a

precision positioning, navigation, or timing system. The M12+ is capable of providing autonomous

position, velocity, and time information over a standard serial port. The minimum usable system

combines the M12+ receiver, antenna, and an intelligent system controller device.

Interface Protocols

The M12+ receiver has either one (M12+ Timing Receiver) or two (M12+ Positioning Receiver)

serial data ports. The first port provides the main control and data path between the M12+ and

the system controller. The second port on the M12+ positioning receiver is dedicated to RTCM

DGPS correction inputs to the receiver. Refer to table below for the interface protocol parameters.

Table 3.6: M12+ Oncore Interface Protocols

Format Motorola Binary NMEA 0183 RTCM SC-104

Type Binary ASCII

Type 1 or 9

messages

Direction In/Out In/Out In

Port 1 1 2

Baud Rate 9600 4800 2400, 4800,9600

Parity None None None

Data Bits 8 8 8

Start/Stop bits 1/1 1/1 1/1

Serial Input/Output

The serial interface pins, RxD and TxD, are the main signals available for user connection. A

ground connection is also required to complete the serial interface. The M12+'s serial port

operates under interrupt control. Incoming commands and data are stored in a buffer that is

serviced once a second by the receiver's operating program. There is no additional protection or

signal conditioning besides the protection designed into the microprocessor since the RxD and

TxD pins are connected to the microprocessor directly. TxD and RxD are standard inverted serial

signals with 3V voltage swings.

Note: THE M12+ SERIAL PORTS ARE NOT 5V LOGIC COMPLIANT

For input signals, minimum input high voltage is 2V and the maximum input high voltage is 3V.

Minimum input low voltage is 0 V and the maximum input low voltage is 0.8 V. For output signals,

minimum output high voltage is 2.4 V and the maximum output low voltage is 0.5 V. This interface

is not a conventional RS-232 interface that can be connected directly to a PC serial port, an RS-

232 driver/receiver is required to make this connection. The driver/receiver provides a voltage

shift from the 3V outputs to a positive and negative voltage (typically +/- 8V), and also has an

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