Motorola M12 Oncore User's Guide download pdf (Page 33)

Chapter 3 – Receiver Description

Motorola GPS Products - Oncore User’s Guide

TTL OUTPUT

The serial interface signals, RXD and TXD, are available for user connection. A

ground signal is also required to complete the serial interface. There is no additional

protection or signal conditioning besides the internal protection of the

microprocessor since they are connected to the microprocessor directly. TXD and

RXD are regular TTL signals with voltage ranges from (0v-3v or 0v-5v depending on

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

input high voltage is 5 V. 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 connect to a PC (which

are normally equipped with an RS232 interface) directly. An RS-232 driver/receiver is

required to make this connection. The driver/receiver provides a voltage shift from 0

to 5 V to a positive and negative voltage (for example, ñ10 V), and also has an

inversion process in it. Some RS-232 driver/receiver integrated circuits (ICs)-for

example; Motorola's MC145407will provide all these functions with only a +5 V

supply.

TTL 0 V to 0.8V = logic

0 2.4 V to 5.0 V = logic 1

RS-232 -5 V to -15 V = logic 1

5 V to 15 V = logic 0

NOTE: 50 pf maximum capacitance on TTL level output

Revision 5.0 08/30/02

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Motorola M12 Oncore User's Guide Page 33