Quectel GSM UART Port Istruzioni per l'installazione e il funzionamento

Quectel Cellular Engine

GSM UART Port

Application Note

GSM_UART_Application_Note_V1.0

GSM UART Port Application Note

GSM_UART_Application_Note_V1.0 - 1 -

Document Title

GSM UART Port Application Note

Version

1.0

Date

2009-06-26

Status

Release

Document Control ID

GSM_UART_Application_Note_V1.0

General Notes

Quectel offers this information as a service to its customers, to support application and

engineering efforts that use the products designed by Quectel. The information provided is

based upon requirements specifically provided to Quectel by the customers. Quectel has not

undertaken any independent search for additional relevant information, including any

information that may be in the customer’s possession. Furthermore, system validation of this

product designed by Quectel within a larger electronic system remains the responsibility of

the customer or the customer’s system integrator. All specifications supplied herein are

subject to change.

This document contains proprietary technical information which is the property of Quectel

Limited., copying of this document and giving it to others and the using or communication of

the contents thereof, are forbidden without express authority. Offenders are liable to the

a utility model or design. All specification supplied herein are subject to change without

notice at any time.

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GSM UART Port Application Note

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Contents

Contents ............................................................................................................................................2

0. Revision history ............................................................................................................................5

1. Introduction...................................................................................................................................6

2. Connection ....................................................................................................................................7

3. Level Shifter..................................................................................................................................8

3.1. Communicate with DTE......................................................................................................8

3.2. Communicate with the RS-232 port of PC..........................................................................9

4. Firmware Upgrade ......................................................................................................................10

5. Flow control ................................................................................................................................12

5.1. Software flow control (XON/XOFF flow control)............................................................12

5.2. Hardware flow control (RTS/CTS flow control)...............................................................12

6. Control Signals............................................................................................................................13

6.1. DCD ..................................................................................................................................13

6.2. DTR...................................................................................................................................13

6.3. RI.......................................................................................................................................14

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GSM UART Port Application Note

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Table Index

TABLE 3: LOGIC LEVELS OF THE UART PORT ...............................................................................8

TABLE 2:THE VOLTAGE OF RS-232 ...................................................................................................9

TABLE 3: RI RESPONSES ...................................................................................................................14

TABLE 4: AT+QINDRI INDICATES RI WHEN USING URC ............................................................15

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GSM UART Port Application Note

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Figure Index

FIGURE 1: CONNECTING TXD AND RXD.........................................................................................7

FIGURE 2: CONNECTING ALL SIGNALS...........................................................................................7

FIGURE 3: THE REFERENCE LEVEL SHIFTER BY USING OPEN DRAIN OUTPUT BUFFER....8

FIGURE 4:THE REFERENCE LEVEL SHIFTER BY USING BIPOLAR TRANSISTOR...................9

FIGURE 5:THE REFERENCE LEVEL SHIFTER BY USING SP3238E FOR COMMUNICATING

WITH PC .........................................................................................................................................9

FIGURE 6: THE CONNECTION FOR FIRMWARE UPGRADE........................................................ 11

FIGURE 7: DTR FOR WAKING UP.....................................................................................................13

FIGURE 8: BEHAVIOURS OF RI ........................................................................................................15

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GSM UART Port Application Note

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0. Revision history

Revision

Date

Author

Description of change

1.0

2009-06-25

Jay XIN / Ken JI

Initial

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GSM UART Port Application Note

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1. Introduction

This document describes the UART port of Quectel GSM module and how to use it in

customer’s application design. This document can help you quickly understand the UART

port of the module.

Note: AT command can be input through UART port only after module is powered

on and the Unsolicited Result Code “RDY” is output.

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GSM UART Port Application Note

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2. Connection

Data Terminal Equipment (DTE) communicates with the module through its main UART

port. The voltage level of UART port interface is 2.8 Volts. If the voltage level of DTE’s

UART pins doesn’t match with the module, level shifter circuit should be inserted. ,

The UART pins include TX data (TXD), RX data (RXD), Request To Send (RTS), Clear To

Send (CTS), Data Terminal Ready (DTR). Data Carrier Detect (DCD) and Ring Indicator

(RI). Not all UART pins are necessary in customer’s application. If the module is used as a

modem, all pins are needed. The modem control signal RI can be used to indicate to the

DTE that a call or Unsolicited Result Code (URC) is received. Hardware handshake using

the RTS and CTS signals and XON/XOFF software flow control are both supported.

Figure 1: Connecting TXD and RXD

Figure 2: Connecting all signals

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3. Level Shifter

Normally, the voltage of VDD_EXT is 2.8V and the DC characteristics of UART port are

listed in Table 3.

Table 1: Logic levels of the UART port

Symbol

MIN

MAX

Unit

VIL

0.67

VIH

1.7

VDD_EXT+0.3

VOL

0.34

VOH

2.0

VDD_EXT

NOTE: If the voltage level of UART pins in DTE and the module doesn’t match with each

other, level shifter circuit should be inserted.

3.1. Communicate with DTE

It is recommended to design the level shift circuit by choosing open drain output buffer

(e.g. NC7WZ07) or discrete transistor.

Note:VDD_EXT is supplied by the module(2.8V). VCC_MCU is the voltage for host

MCU UART interface.

Figure 3: The reference level shifter by using open drain output buffer

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Figure 4:The reference level shifter by using bipolar transistor

3.2. Communicate with the RS-232 port of PC

Table 2:The voltage of RS-232

Logic level

Transmitter capable

Receiver capable

Unit

Logic 0

+5~+15

+3~+25

Logic 1

-5~-15

-3~-25

Undefined

-3~+3

It is suggested to design the level shifter by using RS-232 transceivers, e.g. SP3238E or

MAX3221.

Figure 5:The reference level shifter by using SP3238E for communicating with PC

If only the RXD and TXD pins need to be connected, MAX3221 could be chosen for the level

shifter.

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