Quectel GSM UART Port Installation and operating instructions

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.
Copyright
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
payment of damages. All rights reserved in the event of grant of a patent or the registration of
a utility model or design. All specification supplied herein are subject to change without
notice at any time.
Copyright © Shanghai Quectel Wireless Solutions Co., Ltd. 2009
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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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GSM UART Port Application Note
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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
0.67
V
VIH
1.7
VDD_EXT+0.3
V
VOL
0
0.34
V
VOH
2.0
VDD_EXT
V
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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GSM UART Port Application Note
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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
V
Logic 1
-5~-15
-3~-25
V
Undefined
-3~+3
V
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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