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Neo_M680
User Manual
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Neoway Neo_M680 User Manual

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Neo_M680 GPRS Module
Hardware User Guide
Version 1.4
Copyright © Neoway Technology Co., Ltd
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Copyright © Neoway Technology Co., Ltd 2014. All rights reserved.
No part of this document may be reproduced or transmitted in any form or by any means without prior written consent of Shenzhen Neoway Technology Co., Ltd.
is the trademark of Neoway Technology Co., Ltd.
All other trademarks and trade names mentioned in this document are the property of their respective holders.
Notice
This document is intended for system engineers (SEs), development engineers, and test engineers. The information in this document is subject to change without notice due to product version update or
other reasons. Every effort has been made in preparation of this document to ensure accuracy of the contents, but all
statements, information, and recommendations in this document do not constitute a warranty of any kind, express or implied.
Neoway provides customers complete technical support. If you have any question, please contact your account manager or email to the following email addresses:
Sales@neoway.com.cn Support@neoway.com.cn
Website: http://www.neoway.com.cn
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Issue
Changes
Revised By
Date
V1.0
Initial draft
Qiao Naiwei
2013-10
V1.1
Modified the description of some pins
Qiao Naiwei
2014-02
V1.2
Modified the PCB encapsulation and definition of several pins
Qiao Naiwei
2014-04
V1.3
Optimized the table structure of pin definition and interface description.
Added chapter about electric features and reliability.
Added RF feature description.
Qiao Naiwei
2014-05
V1.4  Optimize the pictures.
Qiao Naiwei
2014-06
Revision Record
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Contents
About This Document ......................................................................................................... 1
1 Introduction to M680 ........................................................................................................ 1
1.1 Overview ..................................................................................................................................... 1
1.2 Block Diagram ............................................................................................................................ 1
1.3 Specifications .............................................................................................................................. 2
2 Pin Description and PCB Foot Print .............................................................................. 4
2.1 Specifications and Encapsulation ................................................................................................ 4
2.2 Pin Definition .............................................................................................................................. 5
2.3 PCB Foot Print ............................................................................................................................ 8
3 Interface Design................................................................................................................. 9
3.1 Power Supply and Switch Interfaces ........................................................................................... 9
3.1.1 Design Requirements ......................................................................................................... 9
3.1.2 VDD_EXT ....................................................................................................................... 12
3.1.3 VRTC ............................................................................................................................... 12
3.1.4 Power-On/Off Control and Procedure .............................................................................. 13
3.1.5 RESET .............................................................................................................................. 16
3.2 UART ........................................................................................................................................ 16
3.3 USB Interfaces .......................................................................................................................... 18
3.4 DTR and RING ......................................................................................................................... 19
3.4.1 DTR Pin ........................................................................................................................... 19
3.4.2 RING Signal Indicator...................................................................................................... 20
3.5 SIM Card Interface .................................................................................................................... 20
3.6 Running LED Indicator ............................................................................................................. 22
3.7 Audio Interface .......................................................................................................................... 23
3.8 RF Interface ............................................................................................................................... 26
3.8.1 RF Design and PCB Layout ............................................................................................. 26
3.8.2 Recommended RF Connection ......................................................................................... 28
4 Electric Features and Reliability ..................................................................................... 29
4.1 Electric Feature ......................................................................................................................... 29
4.2 Temperature ............................................................................................................................... 29
4.3 Current....................................................................................................................................... 30
4.4 ESD Protection .......................................................................................................................... 30
5 RF Features ....................................................................................................................... 32
5.1 Work Band ................................................................................................................................. 32
5.2 Transmitting Power and Receiving Sensitivity ......................................................................... 32
5.2.1 Transmitting Power .......................................................................................................... 32
5.2.2 Receiving Sensitivity ........................................................................................................ 33
6 Mounting the Module onto the Application Board.................................................. 34
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7 Package .............................................................................................................................. 34
8 Abbreviations ................................................................................................................... 35
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Table of Figures
Figure 2-1 Top view of the M680 module ............................................................................................... 4
Figure 2-2 PCB foot print recommended for M680 (unit: mm) .............................................................. 8
Figure 3-1 Current peaks and voltage drops ............................................................................................ 9
Figure 3-2 Capacitors used for the power supply .................................................................................. 10
Figure 3-3 Reference design of power supply control ................................................................ ........... 10
Figure 3-4 Reference design of power supply controlled by p-MOSFET ..............................................11
Figure 3-5 Reference designs of separated power supply ...................................................................... 12
Figure 3-6 VRTC reference design ........................................................................................................ 13
Figure 3-7 Power-on procedure ............................................................................................................. 13
Figure 3-8 Power-off procedure............................................................................................................. 14
Figure 3-9 Reference circuit for power-on/off control .......................................................................... 14
Figure 3-10 Reference circuit for power-on/off controlled by high level .............................................. 15
Figure 3-11 Reset circuit with triode separating .................................................................................... 16
Figure 3-12 Signal connection between DCE and DTE ........................................................................ 16
Figure 3-13 Recommended circuit for the communication between 3.3V MCU and UART ................ 17
Figure 3-14 Recommended circuit for the communication between 5V MCU and UART ................... 18
Figure 3-15 USB circuit ........................................................................................................................ 19
Figure 3-16 RING indicator for incoming call ...................................................................................... 20
Figure 3-17 RING indicator for SMS .................................................................................................... 20
Figure 3-18 Reference design of SIM card interface ............................................................................. 21
Figure 3-19 Reference of SIM card socket ............................................................................................ 21
Figure 3-20 LED indicator..................................................................................................................... 22
Figure 3-21 Reference design of single-end input MIC interface .......................................................... 23
Figure 3-22 Reference design of MIC differential connections ............................................................. 24
Figure 3-23 Reference design for common audio input ........................................................................ 24
Figure 3-24 Reference design for receiver output ................................................................................. 25
Figure 3-25 Reference design for speaker output .................................................................................. 25
Figure 3-26 Reference design for earphone output ................................................................ ................ 26
Figure 3-27 Coupling capacitor interfacing ........................................................................................... 26
Figure 3-28 Reference design for antenna interface .............................................................................. 27
Figure 3-29 RF layout reference ............................................................................................................ 27
Figure 3-30 Encapsulation specifications of Murata RF connector ....................................................... 28
Figure 3-31 RF connections................................................................................................................... 28
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Table of Tables
Table 1-1 M680 specifications................................................................................................................. 2
Table 2-1 M680 pin definition ................................................................................................................. 5
Table 3-1 Power supply and switch interface .......................................................................................... 9
Table 3-2 UART .................................................................................................................................... 16
Table 3-3 USB interface ........................................................................................................................ 18
Table 3-4 DTR and RING pins .............................................................................................................. 19
Table 3-5 SIM Card Interface ................................................................................................................ 20
Table 3-6 LED indicator ........................................................................................................................ 22
Table 3-7 Audio interface ...................................................................................................................... 23
Table 4-1 Electric feature of the module ............................................................................................... 29
Table 4-2 Temperature Feature .............................................................................................................. 29
Table 4-3 Current feature ................................................................ ....................................................... 30
Table 4-4 ESD feature of the module .................................................................................................... 31
Table 5-1 Work band ............................................................................................................................. 32
Table 5-2 Transmitting power (GSM800&EGSM900) ......................................................................... 32
Table 5-3 Transmitting power (DCS1800&PCS1900) .......................................................................... 33
Copyright © Neoway Technology Co., Ltd
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About This Document

This document defines the features, indicators, and test standards of the M680 module and provides reference for the hardware design of each interface. With Neo_M680 GPRS Module AT Command Set, this user guide can help you complete wireless communication application easily.

1 Introduction to M680

M680 is a compact wireless GSM/GPRS module that supports downlink EDGE. It can provide functions of high-quality voice, SMS, and data services and is widely used in industrial and civil fields.

1.1 Overview

Neoway M680 module adopts 83-pin LGA encapsulation and its dimensions are 18 mm x 15 mm x 2.1 mm, which can meet most customers' requirements. It provides customers the following hardware resources:
UART interfaces, used for data communication, firmware updating and commissioning, and
supporting hardware flow control
Audio interfaces: two lines of MIC input (one differential single input and one sing-ended signal
input); EAR/SPK/REC output
10-bit ADC input, voltage ranging from 0 V to 2.8 V Adapting to 1.8 V and 3.0 V SIM card Supporting RING/LIGHT/DTR (sleep mode) functions Supporting time updating and timing power-on/off Supporting firmware updating and commissioning via USB interface

1.2 Block Diagram

The M680 module consists of baseband controller, Flash ROM, RF section, application interfaces, etc. All sections coordinate with each other to provide such communication functions as GPRS data and voice.
The following figure shows the block diagram of M680.
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Specifications
Description
Band
GSM850/EGSM900/DCS1800/PCS1900 MHz dual-band/quad-band Supporting band locking
Sensitivity
< -107 dBm
Max. transmit power
GSM850/EGSM900 Class4(2W)
DCS1800/PCS1900 Class1(1W)
Protocol
Supporting GSM/GPRS Phase 2/2+
AT  GSM07.07
Extended AT commands
VBAT
VRTC
Digital Interface
USB
UART
ON/OFF
Power
Manager
RF transceiver
FLASH
Digital
Baseband
Analog
Baseband
26 MHz CrystalRF Front-end-module
SIM
ADC
SIM
PC
Audio Interface
EAR
SPK
REC
MIC

1.3 Specifications

Table 1-1 M680 specifications
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Audio
Available audio coding:
HR
FR
EFR
AMR Supporting echo suppression Supporting recording and DTMF check function
SMS  TEXT/PDU
Supporting SMS message receiving and transmitting and alert for new
SMS messages
Supporting SMS message management: reading/deleting/storage/list
GPRS feature
GPRS CLASS 12
Max. theoretic uplink rate: 85.6 Kbit/s
Max. theoretic downlink rate: 85.6 Kbit/s
Built-in TCP/IP protocol, supporting multiple links
Supporting server and client modes
Circuit Switch Data
CSD data service
USSD
Supplementary service
Call forwarding (CFB, CFNA, CFU)
Call waiting
Call holding and multi-way calling
UART
Supporting hardware flow control, RTS and CTS controlled via AT
commands
Supporting multiplexing
Supporting AT sending, data transmission, and software download
Supporting baudrate from 1200 bit/s to 115200 bit/s
RTC
Supporting real-time clock and time updating
Supporting timing power-on/off
CPU
ARM7-EJ@360MHz
Antenna feature
50 Ω impedance
Operating temperature
-40℃to +85℃
Operating voltage
3.5 V to 4.3 V (3.9 V is recommended)
Peak current
Max 2.0 A
Idle current
18 mA
Current in sleep mode < 2 mA (live network)
< 1 mA (instrument, DRX=9)
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2 Pin Description and PCB Foot Print

Specifications
M680
Dimensions
18 mm x 15 mm x 2.1 mm (H x W x D)
Weight
1.2 g
Encapsulation
83-pin LGA
GPRS_ANT
8
7
6
5
4
3
2
16
15
14
13
12
11
10
9
18
19
20
17
ON/OFF
SPKP
SPKN
MIC0P
MIC0N
EAR_L
EAR_R
MIC1
RECN
RECP
NC
NC
NC
NC
NC
NC
GND
NC
SIM_CLK
SIM_DATA
NC
NC
NC
NCNCNC
GND
NC
GND
NC
NC
RTS
CTS
VDD_EXT
URXD
UTXD
NC
NC
DTR
RING
LIGHT
RESET
GND
VRTC
VBAT
VBAT
VBAT
ADC_IN
NC
NC
NC
NC
NC
NC
NC
GND
GND VBAT GND GND
GND
GND
GND GND
GND
USB_DM
USB_DP
GND
NC
VBUS
NC NC NC NC
NC NC NCNCNCNC
SIM_RST
VSIM
1
22
23
21
28
29
27
26
25
24
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
46
45
47
48
49
5
0
51
52
53
54
55
56
57
58
59
60 61 62 63
6471
65
66676869
70
72737475767
7
8
3
8
2
8
1
7
9
7
8
8
0
USB
NC
Power
GND SIM UART
Audio ADC GPRS_ANT Other

2.1 Specifications and Encapsulation

Figure 2-1 Top view of the M680 module
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2.2 Pin Definition

Pin
Name
I/O
Function
Reset
Status
Level Feature
(V)
Remarks
Power Supply and Switch Interfaces
57, 58, 59, 68
VBAT
P
Main power supply input
3.5 V to 4.3 V (3.9 V is recommended)
36 VDD_EXT
P
2.8 V power supply output
Supply power for IO level shifting circuit. Load capability: less than 50 mA
41 VRTC
P
RTC power supply
2.8 V, maximum charging output current 2 mA
18, 29, 31, 46, 48, 60, 63~67, 69~71
GND
P
Ground
1 ON/OFF
DI
On/Off input
0＜V
IL
＜
0.6
2.1
＜
V
IH
＜
VBAT
Low level pulse can change the On/Off state.
45 RESET
DI
Reset input
0＜V
IL
＜
0.6
2.1＜V
IH
＜
3.1
Internally pulled up to 2.8 V
Low level reset
Audio Interface
2 SPKP
AO
Positive electrode of speaker output
Maximum 800 mW@8Ω
3 SPKN
AO
Negative electrode of speaker output
4 MIC0P
AI
Positive electrode of MIC0 output
Vpp≤200 mV 5
MIC0N
AI
Negative electrode of MIC0 output
6 EAR_L
AO
Left sound channel of the earphone output
16/32Ω earphone
driving output
7 EAR_R
AO
Right sound channel of the earphone output
9
MIC1
AI
MIC1 output
Table 2-1 M680 pin definition
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10 RECN
AO
Negative electrode of receiver output
32 Ω receiver driving output
11 RECP
AO
Negative electrode of receiver output
UART Interface
34
RTS
DI
Request to send
I/PD
0＜V
IL
＜
0.6
2.1＜V
IH
＜
3.1
0＜V
OL
＜
0.42
2.38＜V
OH
＜
2.8
With 47K pull-up inside
35
CTS
DO
Clear to send
I/PD
37
URXD
DI
UART data receive
I/PU
38 UTXD
DO
UART data transmit
SIM Card
19 SIM_CLK
DO
SIM card clock output
0
＜
V
IL
＜
0.25*VSIM，
0.75*VSIM
＜
V
IH
＜
VSIM
0
＜
V
OL
＜
0.15*VSIM
0.85*VSIM
＜
V
OH
＜
VSIM
Compatible with
1.8/3.0 V SIM card
20
SIM_DATA
DI/O
SIM card data IO
21 SIM_RST
DO
SIM card reset output
22 VSIM
P
SIM card power supply output
LED Indicators
44
LIGHT
DO
Status LED
I/PD
2.8 V/4 mA output
Sleep Mode Controlling
42
DTR
DI
Signal for controlling sleep mode
I/PD
0＜V
IL
＜
0.6
2.1＜V
IH
＜
3.1
0＜V
OL
＜
0.42
2.38＜V
OH
＜
2.8
Low level by default Used together with
AT commands SMS and Incoming Call Ring
43
RING
DO
Ring output
I/PD
0＜V
IL
＜
0.6
2.1＜V
IH
＜
3.1
0＜V
OL
＜
0.42
2.38＜V
OH
＜
2.8
Detect incoming SMS messages or calls
ADC Detecting
56 ADC_IN
AI
10-bit ADC input
Detectable voltage range: 0 V to 2.8 V
GPRS Antenna
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47 GPRS_ANT
AI/O
GPRS antenna interface
50 Ω impedance USB Interfaces
61
USB_DM
DI/O
USB interface differential data cable
Complying with the USB1.1 standard
Used for firmware download
62
USB_DP
DI/O
79
VBUS
AI
USB voltage test
Reserved Pins
8, 12-17, 23-28, 30, 32, 33, 39, 40, 49~55, 72-78, 80~83
NC
Must be left disconnected.
Cannot connect to power supply or ground.
P: indicates power supply pins NC: indicates pins that are not supported and must not be connected DI: indicates digital signal input pins DO: indicates digital signal output pins I/PD: indicates digital signal input pins with pull-down I/PU: indicates digital signal input pins with pull-up AI: indicates analogy signal input pins AO: indicates analogy signal output pins
The maximum input voltage at all IO ports (including peak signal current) cannot exceed 3.1 V because the module uses a 2.8 V IO power system. In the application of the module, the IO output voltage from the
3.3 V power supply system of the external circuit might greatly overshoot 3.1 V due to the signal integrity design. In this situation, the IO pins of the module might be damaged if the IO signals are connected to the IO port on the 2.8-V system. To rectify this issue, take measures to match the level. For details, see the Section 3.2 UART.
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2.3 PCB Foot Print

0.5
1.0
0.5
1.0
18.0
15.0
1.7
1.7
1.1
1.1
6.65
1.7
1.7
1.80
1.5 4.4
8.35
5.45
2.0
1.01.3
0.6
0.7
8.5
LGA packaging is adopted to package the pins of the M680 module. Figure 2-2 shows the recommended PCB foot print.
Figure 2-2 PCB foot print recommended for M680 (unit: mm)
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3 Interface Design

Signal
I/O
Function
Remarks
VBAT
P
Main power supply input
3.5 V to 4.3 V (3.9 V is recommended)
VDD_EXT
P
2.8 V power supply output
Loading capability < 50 mA
VRTC
P
RTC power supply input
2.8 V
ON/OFF
DI
On/Off input
Low level pulse can change the On/Off state.
RESET
DI
Module reset input
Reset at low level Min. 50 ms 100 ms is recommended
Keep above 3.5 V
Keep above 3.5 V
3.5 V
3.5 V
0 ms
0 ms
3.7 ms
3.7 ms
7.4 ms
7.4 ms
10.7 ms
10.7 ms
T
T
2.0 A
2.0 A
Voltage
Voltage
Input
Current
Input
Current
3.9 V
3.9 V

3.1 Power Supply and Switch Interfaces

Table 3-1 Power supply and switch interface

3.1.1 Design Requirements

VBAT is the main power supply of the module. Its input voltage ranges from 3.5 V to 4.3 V and the preferable value is 3.9V. In addition to digital signals and analog signals, it supplies power for RF power amplifier.
The performance of the VBAT power supply is a critical path to module's performance and stability. The peak input current at the VBAT pin can be up to 2 A when the signal is weak and the module works at the maximum transmitting power. The voltage will encounter a drop in such a situation. The module might restart if the voltage drops lower than 3.5 V.
Figure 3-1 Current peaks and voltage drops
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Figure 3-2 shows a recommended power supply design for the module.
Power Supply GPRS Module
Close to the pin of the module
D1
C1 C2 C3 C4
VBAT
Current testing point
I_max
C5
VCC_IN_5V
GPRS_EN
VBAT
100 uF
TAN
0.1 uF
TVS
5V
10 uF
470uF
TAN
10K
4.75K
VOUT
MIC29302WU
EN
VIN ADJ
0.1 uF
100pF
33pF
Figure 3-2 Capacitors used for the power supply
In the circuit, you can use TVS at D1 to enhance the performance of the module during a burst. SMF5.0AG (Vrwm=5V&Pppm=200W) is recommended. A large bypass tantalum capacitor (220 μF or 100 μF) or aluminum capacitor (470 μF or 1000 μF) is expected at C1 to reduce voltage drops during bursts together with C2 (10 μF capacitor). In addition, you need to add 0.1 μF, 100 pF, and 33 pF filter capacitors to enhance the stability of the power supply.
A controllable power supply is preferable if used in harsh conditions. The module might fail to reset in remote or unattended applications, or in an environment with great electromagnetic interference (EMI). You can use the EN pin on the LDO or DC/DC chipset to control the switch of the power supply as shown in Figure 3-3.
MIC29302WU in the following figure is an LDO and outputs 3 A current to ensure the performance of the module.
Figure 3-3 Reference design of power supply control
The alternative way is to use a p-MOSFET to control the module's power, as shown in Figure 3-4. When the external MCU detects the exceptions such as no response from the module or the disconnection of GPRS, power off/on can rectify the module exceptions. In Figure 3-4, the module is powered on when GPRS_EN is set to high level.
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Figure 3-4 Reference design of power supply controlled by p-MOSFET
Q2 is added to eliminate the need for a high enough voltage level of the host GPIO. In case that the GPIO can output a high voltage greater than VDD_IN_3.9V - |V
GS(th)
|, where V
is the Gate Threshold Voltage,
GS(th)
Q2 is not needed. Reference components:
Q1 can be IRML6401 or Rds(on) p-MOSFET which has higher withstand voltage and drain current.
Q2: a common NPN transistor, e.g. MMBT3904; or a digital NPN transistor, e.g. DTC123. If digital transistor is used, delete R1 and R2.
C3: 470 uF tantalum capacitor rated at 6.3V; or 1000 uF aluminum capacitor. If lithium battery is used to supply power, C3 can be 220 uF tantalum capacitor.
Protection
Place a TVS diode (V applications. For some stable power supplies, zener diodes can decrease the power supply overshoot. MMSZ5231B1T1G from ONSEMI and PZ3D4V2 from Prisemi are options.
=5 V) on the VBAT power supply to ground, especially in automobile
RWM
Trace
The trace width of primary loop lines for VBAT on PCB must be able to support the safe transmission of 2A current and ensure no obvious loop voltage decrease. Therefore, the trace width of VBAT loop line is required 2 mm and the ground should be as complete as possible.
Separation
As shown in Figure 3-1, the GPRS module works in burst mode that generates voltage drops on power supply. And furthermore this results in a 217 Hz TDD noise through power (One of the way generating noise. Another way is through RF radiation). Analog parts, especially the audio circuits, are subjected to this noise, known as a "buzz noise" in GSM systems. To prevent other parts from being affected, it's better
Copyright © Neoway Technology Co., Ltd
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to use separated power supplies. The module shall be supplied by an independent power, like a DC/DC or
Other circuit
DC-DC/LDO
GPRS
module
DC-DC/LDO
Power
Input
Other circuitDC-DC/LDO
GPRS
module
Power
Input
10 uH
Reference Design (a) Reference Design (b)
LDO. See Figure 3-5. DC/DC or LDO should output rated peak current larger than 2 A. The inductor used in Reference Design (b), should be a power inductor and have a very low resistance. 10
uH with average current ability greater than 1.2A and low DC resistance is recommended.
Figure 3-5 Reference designs of separated power supply
Never use a diode to make the drop voltage between a higher input and module power. Otherwise,
Neoway will not provide warranty for product issues caused by this. In this situation, the diode will obviously decrease the module performances, or result in unexpected restarts, due to the forward voltage of diode will vary greatly in different temperature and current.
EMC Considerations
Place transient overvoltage protection components like TVS diode on power supply, to absorb the power surges. SMAJ5.0A/C could be a choice.

3.1.2 VDD_EXT

It is recommended that VDD_EXT is only used for interface level transformation. VDD_EXT can output
2.8 V and 50 mA. It stops output after the module is shut down.

3.1.3 VRTC

VRTC is the external power supply pin of RTC inside the module. It can be connected to external battery or supercapacitor. When VBAT works properly, VRTC outputs 2.8 V and maximum 2 mA and can be connected to current limiting resistor or supercapacitor to charge. When VBAT is disconnected, the module can discharge the battery or capacitor to supply power for RTC in short time. Leave it disconnected if not used.
Figure 3-6shows the reference design of the VRTC power supply.
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Figure 3-6 VRTC reference design
Backup
battery
GPRS Module
RTC
Circuit
Capacitor
VRTC
1.5K
VBAT
ON/OFF
VDD_EXT
UART
1.2s
3s
300 ms

3.1.4 Power-On/Off Control and Procedure

Prior to turning on the module, power on the host MCU and finish the UART initialization. Otherwise conflictions may occur during initialization, due to unstable conditions.
ON/OFF is a low level pulse active input, used to turn on or off the module.
Power-On Procedure
While the module is off, drive the ON/OFF pin to ground for at least 1.2 second and then release, the module will start. An unsolicited message (+EIND: 128) will be sent to host through UART port, indicating that the module is powered on and can respond to AT commands.
When you design your program, you can use the unsolicited message (+EIND: 128) to check whether the module is started or reset improperly.
Figure 3-7 Power-on procedure
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Power-Off Procedure
VBAT
ON/OFF
VDD_EXT
UART
2 s
500 ms
GPRS Module
ON/OFF
TVS
S 1
While the module is on, drive the ON/OFF pin to ground for at least 500 ms and then release, the module will try to detach to network and normally 2 seconds later it will shut down. Another approach to turn off the module is using AT commands. For details, see Neo_M680 GPRS Module AT Commands. Figure 3-8 shows the power-off procedure of the module.
Figure 3-8 Power-off procedure
Power-On/Off Control
Figure 3-9 shows a reference circuit for ON/OFF control with inverted control logic.
Figure 3-9 Reference circuit for power-on/off control
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Figure 3-10 Reference circuit for power-on /off controlled by high level
USER_ON
GPRS Module
ON/OFF
4.7K
47K
R1
R2
In Figure 3-10, high level takes effect for ON/OFF on the user side (USER_ON) after level shifting. R1 and R2 can be adjusted according to the driving capability of the USER_ON pin. Use a common NPN transistor, e.g. MMBT3904; or a digital NPN transistor, e.g. DTC123. If digital
transistor is used, delete R1 and R2.
Level abnormalities at interfaces connected to the external MCU, especially the UART port, might affect the power-on procedure of the module. For example, when a module is turned on, the IO ports of the MCU are still in output status because they have not been initialized completely. The module might fails to start if the UTXD signal (output pin) is forced to pull up or down.
The better way to rescue the module from abnormal condition, is to apply a power OFF-ON procedure, rather than using the ON/OFF control signal. In fact ON/OFF signal is software-dependent.
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3.1.5 RESET

Signal
I/O
Function Description
Remarks
RTS
DI
Request to send
CTS
DO
Clear to send
URXD
DI
UART data receive
UTXD
DO
UART data transmit
RESET
VDD_EXT
4.7K
47K
GPRS Module
DCE
URXD UTXD
DTE
UTXD
URXD
RTS
CTS
CTS
RTS
You can reset the module by keeping the RESET pin low level for more than 100 ms. The pin is pulled up by an internal resistor and the typical high level is 2.8 V. The RESET pin can be left disconnected if not used. If you use 3.3 V IO system, you are advised to separate it by using triode. Please refer to Figure 3-11.
Figure 3-11 Reset circuit with triode separating

3.2 UART

Table 3-2 UART
UART is used for AT commands, data sending/receiving, firmware updating, etc. Figure 3-12 shows the signal connection between the module (DCE) and the terminal (DTE).
Figure 3-12 Signal connection between DCE and DTE
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The UART of M680 works at 2.8 V CMOS logic level. The voltages for input high level should not exceed
Module_URXD
Module_UTXD
VDD_EXT
0.1 uF
47K
RB521S
200
33 pF
33 pF
MCU_UTXD
MCU_URXD
3.1 V. Supported baud rates are 1200, 2400, 4800, 9600, 14400, 19200, 38400, 57600, 115200 bit/s, and the default rate is 115200 bit/s.
If the UART is interfacing with a MCU that has 3.3 V logic levels, it is recommended that you add a level shifting circuit outside of the module.
Figure 3-13 Recommended circuit for the communication between 3.3V MCU and UART
In Figure 3-13, 100 pF filter capacitor should be placed near the receive pin of the module. Resistance (200
Ω to 470 Ω) and capacity (100 pF to 470 pF) can be selected based on the tested signal wave. Great serial
resistance and filter capacity will decrease the signal level, resulting in great signal wave distortion and the low adaptable UART communication baudrate. RB521S-30TE-61, RB521SM-30GJT2R, and LRB521S-30T1G are recommended for separating diode.
When the external MCU adopts 5 V IO system, level shifting is required for both UART receive and transmit. Figure 3-14 shows a reference circuit.
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Figure 3-14 Recommended circuit for the communication between 5V MCU and UART
Signal
I/O
Function
Remarks
VBUS
AI
USB voltage check
4.3 V < VBUS < 7 V, typical value: 5 V
USB_DP
DIO
Positive signal of USB data
USB_DM
DIO
Negative signal of USB data
INPUT
OUTPUT
VCC_IN VCC_OUT
4.7K 10K
Q1
R2 R3
In Figure 3-14, INPUT is connected to TXD of the MCU and VCC_IN is connected to the 5 V power supply of the MCU. OUTPUT is connected to RXD of the module and VCC_OUT is connected to VDD_EXT(2.8V) of the module. If the circuit is far away from the VDD_EXT pin, add a 0.1 μF decoupling capacitor to VDD_EXT.
Level shifting between RXD of the MCU and TXD of the module can be implemented in the same way. The pull-up resistor R3 ranges from 4.7 K to 10 K; R2 ranges from 2 K to 10 K. Resistors are selected based
on the voltage of the power supply and UART baudrate. You can select resistors with great resistance to reduce the power consumption when the power supply has great voltage or the baudrate is low. But, the resistance will affect the quality of the square wave. In addition, the circuit performance is affected by the signal traces during PCB layout.
It is recommended that you choose a high-speed NPN transistor because the Q1 switch rate will affect the wave quality after level shifting. MMBT3904 or MMBT2222 is recommended.
Avoid data produced at UART when the module is powered on. You are advised to send data to the UART 3 seconds after the module is powered on so that the module would not respond wrongly.

3.3 USB Interfaces

Table 3-3 USB interface
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For M680 modules, you can download and commission software through the USB interface. Before that,
Signal
I/O
Function
Remarks
DTR
DI
Signal for controlling sleep mode
Low level by default Left disconnected if not used
RING
DO
Ring output
Left disconnected if not used
GPRS
Module
VBUS
USB_DM
USB_DP
GND
PC
UTXD
URXD
RTS
CTS
VBUS
USB_DM
USB_DP
GND
20
20
connect USB interface to a computer and then power on the module. Figure 3-15 shows the recommended connection between the module and a computer.
Figure 3-15 USB circuit
Parallel a 1 μF filter capacitor on VBUS and place it as close to the pin as possible. You must also add TVS to the VBUS power cable. Use TVS diodes with a capacity of lower than 12 pF for protection on the data cables of USB_DP and USB_DM, and adopt differential signal trace for USB_DP and USB_DM.

3.4 DTR and RING

Table 3-4 DTR and RING pins

3.4.1 DTR Pin

Generally DTR is used for sleep mode control. It works with AT commands. For details, see M680 GPRS Module AT Command Set. Based on the setting of the selected mode, pulling DTR low will bring the
module into sleep mode. In this mode, the idle current is less than 2 mA, the module can also respond to the incoming call, SMS, and GPRS data. The host MCU can also control the module to exit sleep mode by controlling DTR.
Process of entering the sleep mode:
1. Keep DTR high level in working mode. Activate the sleep mode by using the AT+ENPWRSAVE=1
command.
2. Pull DTR low, and the module will enter sleep mode, but only after process and pending data
finished.
3. In sleep mode, the module can be woken up by the events of incoming voice call, received data, or
SMS. Meanwhile the module will send out the unsolicited messages by the interface of RING or UART.
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Upon receipt of the unsolicited messages, the host MCU should pull DTR high firstly, otherwise the
Signal
I/O
Function Description
Remarks
VSIM
P
SIM card power supply output
1.8V/3.0V
SIM_CLK
DO
SIM card clock output
SIM_RST
DO
SIM card reset output
SIM_DATA
DI/O
SIM card data IO
Internal pull-up
4s
250 ms
250 ms
600 ms
module will resume sleep mode shortly. And then the host MCU can process the voice call, received data, or SMS. After processing is finished, pull DTR low again to put the module into sleep mode.
4. Pull DTR high, the module will exit from sleep mode actively, and furthermore enable the UART.
Thus the voice call, received data, or SMS can be processed through UART. After processing finished pull it low again, to take the module back to sleep mode.

3.4.2 RING Signal Indicator

Calling: Once a voice call is coming, UART output "RING" character strings and meanwhile the RING pin outputs 250 ms low pulses at 4s period. After the call is answered, the high level restores.
Figure 3-16 RING indicator for incoming call
SMS: Upon receipt of SMS, the module outputs one 600 ms low pulse.
Figure 3-17 RING indicator for SMS

3.5 SIM Card Interface

Table 3-5 SIM Card Interface
M680 supports 3.0 V and 1.8 V SIM cards. VSIM supplies power for SIM card with 30 mA. SIM_DATA is internally pulled up by a resistor. External pull-up resistor is not needed.
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SIM_CLK can work at several frequencies at 3.25 MHz typically.
20
20
20
1 uF
SIM_DATA
SIM_CLK
SIM_RST
VSIM
GPRS
Module
CLK RST
VCC
VPP
GND
SIM卡
DATA
Figure 3-18 Reference design of SIM card interface
ESD protectors, such as ESD diodes (lower than 33 pF) or ESD varistors, are recommended on the SIM signals, especially in automotive electronics or other applications with badly ESD. In other applications, replace ESD diodes with 27 pF to 33 pF grounding capacitors. The ESD diodes or small capacitors should be close to SIM card.
If you use 6-pin SIM card sockets, MCP-C713(H2.8) is recommended. Figure 3-19 shows its encapsulation.
Figure 3-19 Reference of SIM card socket
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Signal
I/O
Function
Remarks
LIGHT
DO
Indicates running status
2.8 V output, max. 4 mA High level drives the LED indicator
LIGHT
GPRS
Module
1K
LIGHT
GPRS Module
10K
VCC
470
4.7K
SIM card is sensitive to GSM TDD noise and RF interference. So, the PCB design should meet the following requirements:
The antenna should be installed far away from the SIM card and SIM card traces, especially to the
build-in antenna.
The SIM traces on the PCB should be as short as possible and shielded with GND copper.
The ESD diodes or small capacitors should be closed to SIM card on the PCB.

3.6 Running LED Indicator

Table 3-6 LED indicator
The LIGHT pin can output a 4 mA current and 2.8 V voltage, therefore the LED can be directly connected to this pin with a resistor in series. For better luminance, drive the LED with a transistor instead.
Figure 3-20 LED indicator
When the module is running, the LED indicator is driven by the LIGHT to indicate different module status with its various blink behaviors. You can set the blink mode by AT commands. For more details, see Neo_M680 GPRS Module AT Command Set.
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3.7 Audio Interface

Signal
I/O
Function
Remarks
SPKP
AO
Positive electrode of speaker output
Class AB speaker Maximum 0.8 W@8Ω
SPKN
AO
Negative electrode of speaker output
MICP0
AI
Positive electrode of MIC0 output
Vpp≤200 mV MICN0
AI
Negative electrode of MIC0 output
EAR-L
AO
Left sound channel of the earphone output
16/32Ω earphone driving
output EAR-R
AO
Right sound channel of the earphone output
MIC1
AI
Single-end MIC1 input
RECN
AO
Negative electrode of receiver output
32Ω receiver driving
output RECP
AO
Negative electrode of receiver output
GPRS
Module
MIC
33 pF
MIC
Table 3-7 Audio interface
M680 supports multiple lines of audio interfaces to meet customers' requirements for audio. You can switch the audio channels and adjust the volume via AT commands. For details, see Neo_M680 GPRS Module AT Command Set.
Figure 3-21 shows a reference audio interface. The peak voltage routed to MICP/MICN should not exceed 200 mV AC. AGC circuit is integrated inside the module. Electret microphone is suited.
The module can meet the requirements of common handsets with AGC and volume control.
Figure 3-21 Reference design of single-end input MIC interface
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Figure 3-22 Reference design of MIC differential connections
GPRS Module
33 pF
MIC
33 pF
100 pF
MICN
MICP
GPRS Module
33 pF
33 pF
MICN
MICP
MIC_BIAS
Baseband
Circuit
2.2 uF
2.2K
C1
C2
User's
Circuit
R1
R3
R2
R4
·
2.2K
R6
R5
In Figure 3-23, a bias voltage for microphone is provided through MICP and MICN. But if an amplifier is used between the microphone and module, capacitors like C1 and C2, should be placed between the outputs of amplifier and module, to block the bias voltage.
For a peak voltage greater than 200 mV AC, an attenuation circuit comprised of R1-R4 should be used.
Figure 3-23 Reference design for common audio input
In above figures, the audio input circuits are designed to meet the requirements for small audio signal, far away from interference source and masking PCB routing by ground.
Figure 3-24 shows a reference design for the receiver interface, through which a 32 Ω receiver can be driven directly.
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Figure 3-24 Reference design for receiver output
GPRS Module
33 pF
33 pF
100 pF
RECN
RECP
Receiver@32
SPK@8?
GPRS Module
33 pF
33 pF
100 pF
SPKN
SPKP
The maximum output power of SPKP/N is 0.8W@8Ω.
Figure 3-25 Reference design for speaker output
Figure 3-26 shows a reference design for the earphone interface, through which a 16/32 Ω receiver can be driven directly. You are advised to use large capacitors for C1 and C2 to ensure the low frequency response of the audio signals.
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Figure 3-26 Reference design for earphone output
GPRS Module
C2
C1
EAR_R
EAR_L
33pF 33pF
GPRS Module
RECN/SPKN/EAR_R
RECP/SPKP/EAR_L
C1
C2
User's
Circuit
If an external amplifier is used to drive the speakers, coupling capacitors of 2.2 μF to 4.7 μF should be used to block the DC voltage, as shown in Figure 3-27.
Figure 3-27 Coupling capacitor interfacing

3.8 RF Interface

3.8.1 RF Design and PCB Layout

A 50 Ω antenna is required. VSWR ranges from 1.1 to 1.5. The antenna should be well matched to achieve best performance. It should be installed far away from high speed logic circuits, DC/DC power, or any other strong disturbing sources.
For multiple-layer PCB, the trace between the antenna pad of module and the antenna connector, should
have a 50 Ω characteristic impedance, and be as short as possible. The trace should be surrounded by ground
copper. Place plenty of via holes to connect this ground copper to main ground plane, at the copper edge. If the trace between the module and connector has to be longer, or built-in antenna is used, a π-type
matching circuit should be needed, as shown in Figure 3-28. The types and values of C1, L1, and L2 should be verified by testing using network analyzer instrument. If the characteristic impedance is well matched, and VSWR requirement is met, just use a 0 Ω resistor for C1 and leave L1, L2 un-installed.
Avoid any other traces crossing the antenna trace on neighboring layer.
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Figure 3-28 Reference design for antenna interface
GPRS
Module
ANT
C1
GPRS_ANT
L2
L1
The RF traces are wide 0.5 mm; leave space at least 0.5 mm between the coppers. Drill enough grounding holes.
Ensure that the ground pins on both sides of the antenna are grounded completely and they form a complete circle with grounding copper.
On two-layer boards which cannot control resistance properly, the RF route should be as short and smooth as possible and at a width of 0.5 mm; the RF is 0.5 mm away from the ground.
Figure 3-29 shows a two-layer board application. The RF is connected to GSC RF connector through traces on PCB, which is connected to the antenna via cable.
Figure 3-29 RF layout reference
ESD protection is built in module. For special ESD protection, an ESD diode can be placed close to the antenna. But ensure using a low junction capacitance ESD diode. The junction capacitance should be less than 0.5 pF, otherwise the RF signal will be attenuated. RCLAMP0521P from Semtech, or ESD5V3U1U from Infineon, can be used here.
On the PCB, keep the RF signals and RF components away from high-speed circuits, power supplies, transformers, great inductors, the clock circuit of single-chip host, etc.
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3.8.2 Recommended RF Connection

If you adopts RF cables for connections, the GSC RF connector MM9329-2700RA1 from Murata is recommended. Figure 3-30 shows the encapsulation specifications.
Figure 3-30 Encapsulation specifications of Murata RF connector
RF cable can also be connected to the module by soldering. In this manner, you must ensure proper soldering in case of damage that lowers RF performance. Figure 3-31 shows the pictures of these two connections.
Figure 3-31 RF connections
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4 Electric Features and Reliability

Parameter
Minimum Value
Typical Value
Maximum Value
VBAT Vin
3.5 V
3.9 V
4.3 V
Iin / /
2 A
VBUS
4.3 V
5 V
7 V
VDD_EXT Vout
/
2.8 V
/
Iout / /
50 mA
DIO
Vout
2.3 V
2.8 V
3.1 V
Iout / /
4 mA
Vin
-0.3 V
0 V
0.6 V
Iin / /
22.5 uA
Module Status
Minimum Value
Typical Value
Maximum Value
Working
-40℃
25℃
85℃
Storage
-45℃
90℃

4.1 Electric Feature

Table 4-1 Electric feature of the module
If the voltage is too low, the module might fail to start. If the voltage is too high or there is a voltage burst during the startup, the module might be damaged permanently.
If you use LDO or DC-DC to supply power for the module, ensure that it output at least 2 A current.

4.2 Temperature

Table 4-2 Temperature Feature
If the module works in temperature exceeding the thresholds, its RF performance (e.g. frequency deviation or phase deviation) might be worse but it can still work properly.
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4.3 Current

Parameter
Testing Conditions
Testing Result
(Average Current)
Testing voltage
3.9 V Agilent power supply
/
Idle mode
Set the instrument and power on the module.
18 mA
Off leakage current
Power on the module or use AT command to shut the module down.
56 uA
Average network searching current
Set the instrument
.
Start the module. Wait until the module registers the instrument.
60 mA
Sleep mode
On a live network, the module registers the network and then enters the sleep mode.
1.705 mA Set the instrument properly (DRX=9)
987 uA
Voice service
Maximum power level in full rate mode
GSM850
208.55 mA
EGSM900
198.43 mA
DCS1800
136.71 mA
PCS1900
132.29 mA
GPRS class 12
4TX, 1RX (4Up/1Down)
GSM850
426.58 mA
EGSM900
422.15 mA
DCS1800
269.99 mA
PCS1900
278.38 mA
1TX, 4RX (1Up/4Down)
GSM850
198.74 mA
EGSM900
185.86 mA
DCS1800
144.23 mA
PCS1900
130.57 mA
Table 4-3 Current feature
The data in the above table is typical values obtained during tests in lab. It might be a little bit different in manufacturing. Also, the test results might be various due to different settings or testing methods.

4.4 ESD Protection

Electronics need to pass sever ESD tests. The following table shows the ESD capability of key pins of our module. It is recommended that you add ESD protection to those pins in accordance to the application to ensure your product quality when designing your products.
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Humility: 45%
Testing Point
Contact Discharge
Air Discharge
VBAT
±8 KV
±15 KV
GND
±8 KV
±15 KV
ANT
±8 KV
±15 KV
Cover
±8 KV
±15 KV
RXD/TXD
±4 KV
±8 KV
USB
±4 KV
±8 KV
MIC/SPK/REC/EAR
±4 KV
±8 KV
Others
±4 KV
±8 KV
Temperature: 25℃
Table 4-4 ESD feature of the module
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5 RF Features

Work Band
Uplink
Downlink
GSM850
824~849 MHz
869~894 MHz
EGSM900
880~915 MHz
925~960 MHz
DCS1800
1710~1785 MHz
1805~1880 MHz
PCS1900
1850~1910 MHz
1930~1990 MHz
PCL
Transmitting Power
Threshold Range
5
33 dBm
±2 dBm
6
31 dBm
±3 dBm
7
29 dBm
±3 dBm
8
27 dBm
±3 dBm
9
25 dBm
±3 dBm
10
23 dBm
±3 dBm
11
21 dBm
±3 dBm
12
19 dBm
±3 dBm
13
17 dBm
±3 dBm
14
15 dBm
±3 dBm
15
13 dBm
±5 dBm
16
11 dBm
±5 dBm
17
9 dBm
±5 dBm
18
7 dBm
±5 dBm
19
5 dBm
±5 dBm

5.1 Work Band

Table 5-1 Work band

5.2 Transmitting Power and Receiving Sensitivity

5.2.1 Transmitting Power

Table 5-2 Transmitting power (GSM800&EGSM900)
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Table 5-3 Transmitting power (DCS1800&PCS1900)
PCL
Transmitting Power
Threshold Range
0
30 dBm
±2 dBm
1
28 dBm
±3 dBm
2
26 dBm
±3 dBm
3
24 dBm
±3 dBm
4
22 dBm
±3 dBm
5
20 dBm
±3 dBm
6
18 dBm
±3 dBm
7
16 dBm
±3 dBm
8
14 dBm
±3 dBm
9
12 dBm
±3 dBm
10
10 dBm
±4 Bm
11
8 dBm
±4 Bm
12
6 dBm
±4 Bm
13
4 dBm
±4 dBm
14
2 dBm
±5 dBm
15
0 dBm
±5 dBm
Band
Typical
GSM800&EGSM900
<-107 dBm
DCS1800&PCS1900
<-107 dBm

5.2.2 Receiving Sensitivity

The data in the above tables is obtained by connecting the module to RF test instrument (e.g.
CMU200, CWM500, or Agilent8960) in lab tests. It is for reference only.
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6 Mounting the Module onto the Application Board

M680 is compatible with industrial standard reflow profile for lead-free SMT process. The reflow profile is process dependent, so the following recommendation is just a start point guideline:
Only one flow is supported.
Quality of the solder joint depends on the solder volume. Minimum of 0.15mm stencil thickness is recommended.
Use bigger aperture size of the stencil than actual pad size.
Use a low-residue, no-clean type solder paste.

7 Package

M680 modules are packaged in sealed bags on delivery to guarantee a long shelf life. Package the modules again in case of opening for any reasons.
If exposed in air for more than 48 hours at conditions not worse than 30°C/60% RH, a baking procedure should be done before SMT. Or, if the indication card shows humidity greater than 20%, the baking procedure is also required.
The baking should last for at least 12 hours at 90℃.
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8 Abbreviations

ADC
Analog-Digital Converter
AFC
Automatic Frequency Control
AGC
Automatic Gain Control
AMR
Acknowledged multirate (speech coder)
CSD
Circuit Switched Data
CPU
Central Processing Unit
DAI
Digital Audio interface
DAC
Digital-to-Analog Converter
DCE
Data Communication Equipment
DSP
Digital Signal Processor
DTE
Data Terminal Equipment
DTMF
Dual Tone Multi-Frequency
DTR
Data Terminal Ready
EFR
Enhanced Full Rate
EGSM
Enhanced GSM
EMC
Electromagnetic Compatibility
EMI
Electro Magnetic Interference
ESD
Electronic Static Discharge
ETS
European Telecommunication Standard
FDMA
Frequency Division Multiple Access
FR
Full Rate
GPRS
General Packet Radio Service
GSM
Global Standard for Mobile Communications
HR
Half Rate
IC
Integrated Circuit
IMEI
International Mobile Equipment Identity
LCD
Liquid Crystal Display
LED
Light Emitting Diode
MS
Mobile Station
PCB
Printed Circuit Board
PCS
Personal Communication System
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RAM
Random Access Memory
RF
Radio Frequency
ROM
Read-only Memory
RMS
Root Mean Square
RTC
Real Time Clock
SIM
Subscriber Identification Module
SMS
Short Message Service
SRAM
Static Random Access Memory
TA
Terminal adapter
TDMA
Time Division Multiple Access
UART
Universal asynchronous receiver-transmitter
VSWR
Voltage Standing Wave Ratio
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