TUYA NB-IoT Series Guide

Hangzhou Tuya Inc. NM1 Module Hardware Design Manual
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NM1 Module Hardware Design Manual
NB-IoT Series
Issue: V1.1
Date: 2019-05-06
The Tuya Smart platform is a global intelligent platform, AI and IoT developer platform, and
world-leading voice interaction platform that provides one-stop AI and IoT solutions to meet intelligence
requirements of consumers, manufacturers, OEMs, and retail chain stores. Its solutions cover hardware
access, cloud services, and app software development, forming a closed service loop of AI and
manufacturing. It provides business group technologies and business model upgrade services for
consumer-level smart IoT devices to meet consumers' higher requirements for hardware. Tuya has
always been committed to providing customers with timely and comprehensive services. If you need any
help, contact Tuya headquarters. Tuya's contact information is as follows:
Hangzhou Tuya Inc.
Floor 7, Zheshang Fortune Center, No. 99, Gudun Road, Xihu District, Hangzhou, Zhejiang Province,
China
400-881-8611

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Change History
Date
Version
Change Description
Prepared By
Reviewed By
Approved By
2019-03-01
1.0
This is the first release.
Wang Yanfeng
Wang Yanfeng
Chen Lihuan

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Notice
Copyright Statement
Tuya reserves rights for this document and its content, which is protected by Chinese laws and related
copyright laws in applicable international conventions. No part of this document may be reproduced,
transmitted, distributed, or modified in any form or by any means without prior written consent of Tuya.
Those who violate shall be held liable.
Statement of Non-Guarantee
Tuya does not provide guarantees or presentations of any kind, either express or implied for content in
this document and is not reliable for specific merchantability, applicability, and indirect, special, or
associated losses.
Confidentiality Statement
Information, including attachments in this document, is confidential. Those who receive this document
shall know that it is confidential, not use it for other purposes except the specified one, and not disclose
it to any third party.
Disclaimer
Tuya is not reliable for human injuries or property damages caused by misoperations. You shall develop
products based on the technical specifications and reference design provided in this document. The
information in this document is subject to changes without notice.

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Contents
1 About This Document................................................................................................................................................... 6
1.1 Applicable Scope....................................................................................................................................................6
1.2 Purpose................................................................................................................................................................... 6
1.3 Reference Documents............................................................................................................................................6
1.4 Acronyms and Abbreviations.................................................................................................................................. 6
2 Product Overview..........................................................................................................................................................7
2.1 Package Size........................................................................................................................................................... 7
2.2 Technical Parameters...............................................................................................................................................8
2.3 Product Functions................................................................................................................................................. 9
2.3.1 Baseband Functions..................................................................................................................................... 9
2.3.2 RF Functions................................................................................................................................................. 9
3 Interfaces......................................................................................................................................................................11
3.1 Pin Definition....................................................................................................................................................... 11
3.1.1 Pin Symbols..................................................................................................................................................11
3.1.2 Pin Configuration Diagram.......................................................................................................................11
3.1.3 Pins............................................................................................................................................................... 11
3.2 Electrical Conditions............................................................................................................................................. 15
3.3 Power Interface....................................................................................................................................................15
3.3.1 Power Pins and Grounding....................................................................................................................... 15
3.3.2 Power Supply Requirements..................................................................................................................... 15
3.4 SIM Card Interface............................................................................................................................................. 16
3.4.1 Pins...............................................................................................................................................................16
3.4.2 SIM Card Interface Application................................................................................................................... 16
3.5 SPIs........................................................................................................................................................................17
3.5.1 Pins............................................................................................................................................................... 17
3.5.2 SPI Electrical Parameters and Application.................................................................................................. 17
3.6 I2C Interface.........................................................................................................................................................17
3.6.1 Pins...............................................................................................................................................................17
3.6.2 I2C Interface Electrical Parameters and Application.............................................................................18
3.7 UART Interface................................................................................................................................................... 18
3.7.1 Pins............................................................................................................................................................... 18
3.7.2 UART Interface Electrical Parameters and Application.............................................................................. 18
3.8 USB Interface.......................................................................................................................................................19
3.8.1 USB and Downloading Interface Pins (COM Function Not Supported).................................................... 19
3.8.2 USB and Downloading Interface Application............................................................................................. 20
3.9 Power-On/Power-Off and Reset Interface............................................................................................................ 20
3.9.1 PWRKEY Pin...............................................................................................................................................20
3.9.2 Power-On/Power-Off Interface Application................................................................................................ 20
3.9.3 RESET Pin....................................................................................................................................................21
3.9.4 RESET Interface Application.......................................................................................................................21
4 Design Instructions......................................................................................................................................................21
4.1 General Design Rules and Requirements..............................................................................................................21
4.2 Power Supply Circuit Design................................................................................................................................21
4.3 RF Circuit Design................................................................................................................................................ 21
4.3.1 RF Antenna Circuit Design.......................................................................................................................... 22
4.3.2 Precautions for Initial Antenna Design........................................................................................................ 23
4.4 Suggestions on EMC and ESD Design................................................................................................................. 23
4.5 PCB Solder Pad Design.......................................................................................................................................23
4.6 Thermal Design..................................................................................................................................................... 23
5 Production Instructions................................................................................................................................................24
5.1 Stencil Design........................................................................................................................................................24
5.2 Oven Temperature Curve................................................................................................................................... 24
6 Mechanical Size...........................................................................................................................................................26
6.1 NM1 Module Mechanical Size............................................................................................................................. 26
6.2 Recommended Package Size.................................................................................................................................28

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Figures
Figure 2- 1 Product appearance..................................................................................................................................... 7
Figure 2- 2 Package size diagram (unit: mm)............................................................................................................... 7
Figure 2- 3 System connection framework................................................................................................................... 9
Figure 3- 1 Pin configuration diagram.........................................................................................................................11
Figure 3- 2 Power supply of the NM1 module............................................................................................................15
Figure 3- 3 SIM card interface application..................................................................................................................16
Figure 3- 4 Reference circuit....................................................................................................................................... 17
Figure 3- 5 Reference circuit....................................................................................................................................... 18
Figure 3- 6 Reference circuit....................................................................................................................................... 18
Figure 3- 7 Reference circuit with a level converter...................................................................................................19
Figure 3- 8 Reference circuit with a triode for level conversion................................................................................ 19
Figure 3- 9 Downloading interface application circuit............................................................................................... 20
Figure 3- 10 PWRKEY interface application circuit.................................................................................................. 20
Figure 3- 11 RESET interface application circuit....................................................................................................... 21
Figure 4- 1 Antenna impedance calculation model..................................................................................................... 22
Figure 4- 2 Antenna PCB cabling impedance calculation data...................................................................................23
Figure 5- 1 Recommended stencil strips..................................................................................................................... 24
Figure 5- 2 Over temperature curve............................................................................................................................ 25
Figure 6- 1 Top view (unit: mm)................................................................................................................................. 26
Figure 6- 2 Side view (unit: mm)................................................................................................................................ 26
Figure 6- 3 Transparent view (unit: mm).................................................................................................................... 27
Figure 6- 4 Recommended package size (unit: mm)...................................................................................................28
Tables
Table 1- 1 Reference documents....................................................................................................................................6
Table 1- 2 Acronyms and abbreviations........................................................................................................................ 6
Table 2- 1 Technical parameters of the NM1 module................................................................................................... 8
Table 2- 2 Working frequency bands.............................................................................................................................9
Table 2- 3 Line loss requirements................................................................................................................................10
Table 2- 4 Antenna requirements.................................................................................................................................10
Table 2- 5 Conducted RF transmit power....................................................................................................................10
Table 3- 1 Pin symbols.................................................................................................................................................11
Table 3- 2 Interface pin definition............................................................................................................................... 11
Table 3- 3 Electrical conditions................................................................................................................................... 15
Table 3- 4 Definition and description of SIM card interface signals.......................................................................... 16
Table 3- 5 SPI signal definition................................................................................................................................... 17
Table 3- 6 I2C interface signal definition.....................................................................................................................17
Table 3- 7 UART interface signal definition............................................................................................................... 18
Table 3- 8 USB and downloading interface signal definition..................................................................................... 19
Table 3- 9 PWRKEY signal definition........................................................................................................................ 20
Table 3- 10 RESET signal definition...........................................................................................................................21
Table 5- 1 Over temperature curve parameter settings................................................................................................24

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1 About This Document
1.1 Applicable Scope
This document describes hardware interface specifications, electrical features, mechanical specifications, and
other related information about the NM1 module to help you design and develop NM1 module hardware.
1.2 Purpose
This document provides NM1 module design and development bases. Through this document, you can know the
NM1 module and its technical parameters and develop related functional product or devices.
In addition to functional features and technical parameters, this document also describes the product reliability
test, related test standards, service function implementation process, RF performance indicators, and circuit
design.
1.3 Reference Documents
Table 1- 1 Reference documents
1.4 Acronyms and Abbreviations
Table 1- 2 Acronyms and abbreviations
Document No.
Document Name
NM1 Module Hardware Manual.pdf
NM1 Module Software Manual.pdf
NM1 Module TE-B User Manual.pdf
Acronyms
Full Spelling
ESD
electrostatic discharge
USB
Universal Serial Bus
UART
universal asynchronous receiver/transmitter
SIM
subscriber identity module
SPI
serial peripheral interface
I2C
inter-integrated circuit
I/O
Input/Output
GPIO
General Purpose Input/Output
TDB
To be determined
RTC
real-time clock
ADC
analog to digital converter

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2 Product Overview
NM1 is a compact, high-performance, and low-power NB-IoT series module. It has the following features:
Supports the B1, B3,B5,B8, B20 frequency bands.
Provides the SIM card interface (1.8 V), USB 1.1 interface, UART interface, SPI, I2C interface, and GPIO
interface.
Figure 2- 1 Product appearance
2.1 Package Dimensions
The NM1 module has 66 pins. Its dimensions is 17.7 2.4 mm (H) x 17.7 mm (W) x 15.8 mm (D).
Figure 2- 2 Package dimensions diagram (unit: mm)

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2.2 Technical Parameters
Table 2- 1 describes mechanical features, baseband features, RF features, technical standards, and environment
features of the NM1 module.
Table 2- 1 Technical parameters of the NM1 module
Note:
1. When the NM1 module works at a temperature within the normal operating temperature range1, its performance complies with
3GPP standards.
2. When the NM1 module works at a temperature within the extended operating temperature range2, it works properly, has the
SMS* and data transmission functions, and will not have unrecoverable faults. The RF spectrum and network are not affected.
Several indicators, for example, the output power, may exceed the 3GPP limits. After the operating temperature is restored to the
normal operating temperature, all NM1 module indicators can meet 3GPP standard requirements.
3. A feature with an asterisk (*) is being developed.
Item
Parameter
Specifications
Mechanical
features
Package size and type
17.7 mm x 15.8 mm x 2.6 mm
Stamp hole (52 pins) and base pad (14 pins)
Module
Platform
MT2625
Processor architecture
ARM Cortex-M4
SIM card interface
1.8 V
USB interface
USB 1.1
Voltage
2.1 V to 3.63 V
Working mode
Active: The NM1 module is active and can send and receive data. All functions are
available. An active NM1 module can switch to the idle or PSM mode.
Idle: The NM1 module is in idle state, connected to a network, and can receive paging
messages. An idle NM1 module can switch to the active or PSM mode.
PSM: Only RTC of the module works, and the module is disconnected from the network
and cannot receive paging messages.
The NM1 module is woken up from the PSM mode when the timer expires or the
PWRKEY and PSM_EINT* pins are lowered.
Power-saving
In PSM mode, the NM1 module consumes the minimum power of 5 µA. The PSM mode
is provided to reduce power consumption and prolong the power supply duration of the
battery.
Serial port
Primary serial interface: transmits AT commands and data. The default baud rate is 115.2
kbit/s. It can also be used for firmware upgrade and the baud rate is 921.6 kbit/s.
Debugging serial interface: exports log information for software commissioning.
Auxiliary serial interface: transmits AT commands and data.
Working current
TBD
RTC
Supported
ADC*
The NM1 module has a 10-bit analog-digit conversion input interface to measure the
voltage. This interface works in both active and idle modes.
RI signal*
When the NM1 module receives SMS messages or exports URC, it notifies the DTE
over the RI pin.
Network status
indication*
The NETLIGHT signal indicates the module's network connection status.
RF
Frequency band
B1, B3, B5,B8, B20
Maximum TX power
23±2 dBm
Receiving sensitivity
TBD
Main antenna interface
Supported
Antenna interface
Characteristic impedance of 50 ohms. The antenna is provided by a third party, but not
Tuya.
Technical
standard
Data rate
Single-tone: downlink 25.5 kbit/s and uplink 16.7 kbit/s
Multi-tone*: downlink 25.5 kbit/s and uplink 62.5 kbit/s
Network protocol
UDP/TCP/CoAP/LWM2M/PPP*/SSL*/DTLS*/FTP*/HTTP*/MQTT*/HTTPS*
Environment
feature
Temperature
Normal operating temperature: –35°C to +75°C1
Extended operating temperature: –40°C to +85°C2
Storage temperature: –40°C to +90°C
Application
SMS*
Text and packet data unit (PDU) modes
Upgrade
Upgrade is performed over the primary serial interface.

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2.3 Product Functions
2.3.1 Baseband Functions
The NM1 module baseband includes the USB interface signal, SIM card interface signal, I2C interface signal,
UART interface signal, working status indicator signal, module startup and reset signals, and multiplexing
control signals, power supply, and grounding of multiple GPIO interfaces.
Figure 2- 3 System connection framework
2.3.2 RF Functions
Table 2- 2 Working frequency bands
Note: The NM1 module is being developed to support the frequency bands with an asterisk (*).
Working Frequency Band
Uplink (MHz)
Downlink (MHz)
B1
1920–1980
2110–2170
B3
1710–1785
1805–1880
B5
824–849
869-894
B8
880–915
925–960
B20
832–862
791–821

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Table 2- 3 Line loss requirements
Frequency Band
Requirement
LTE B5, B8, B20
Line loss < 1 dB
LTE B1, B3
Line loss < 1.5 dB
Table 2- 4 Antenna requirements
Item
Requirement
Frequency band
LTE B1, B3, B5,B8, B20
Standing wave ratio (SWR)
≤ 2
Efficiency (%)
≥ 30
Maximum input power (W)
50
Input impedance (ohm)
50
Polarization type
Linear polarization
Note: The NM1 module is being developed to support the frequency bands with an asterisk (*).
Table 2- 5 Conducted RF transmit power
Frequency Band
Maximum Value (dBm)
Minimum Value (dBm)
B1
23±2 dBm
< –39
B3
23±2 dBm
< –39
B5
23±2 dBm
< –39
B8
23±2 dBm
< –39
B20
23±2 dBm
< –39
Note:
1. The designed conducted RF transmit power complies with the NB-IoT protocol in 3GPP Release 13 and Release 14.
2. The NM1 module is being developed to support the frequency bands with an asterisk (*).

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3 Interfaces
3.1 Pin Definition
3.1.1 Pin Symbols
Table 3- 1 Pin symbols
3.1.2 Pin Configuration Diagram
Figure 3- 1 shows the NM1 module's interface pins.
Figure 3- 1 Pin configuration diagram
3.1.3 Pins
Table 3- 2 Interface pin definition
Pin No.
Analog Signal
Definition
Pin Attribute
Input/
Output
Pin Voltage (V)
Remarks
1
AGND
GND
N/A
N/A
N/A
2
GPIO0
GPIO0
N/A
1.8
N/A
Pin Symbol
Description
I
Input
O
Output
I/O
Input/Output

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Pin No.
Analog Signal
Definition
Pin Attribute
Input/
Output
Pin Voltage (V)
Remarks
3
SPI_MISO
Primary device input and
secondary device output
signal
I
1.8
N/A
4
SPI_MOSI
Primary device output
and secondary device
input signal
O
1.8
N/A
5
SPI_SCLK
Serial clock signal
O
1.8
N/A
6
SPI_CS
Chip selection signal
O
1.8
N/A
7
PWRKEY
Lower PWRKEY to
power on the NM1
module.
I
Maximum value of VIL: 0.3 x
VBAT
Minimum value of VIH: 0.7 x
VBAT
N/A
8
GPIO22
GPIO22
N/A
N/A
N/A
9
ADC0
Common analog-digit
conversion interface
I
0–1.4 V
N/A
10
SIM_GND
GND dedicated for the
SIM card
N/A
N/A
N/A
11
SIM_DATA
SIM card data signal
I/O
Maximum value of VIL: 0.25 x
SIM_VDD
Minimum value of VIH: 0.75 x
SIM_VDD
Maximum value of VOL: 0.15 x
SIM_VDD
Minimum value of VOH: 0.85 x
SIM_VDD
N/A
12
SIM_RST
SIM card reset signal
I/O
Maximum value of VOL: 0.15 x
SIM_VDD
Minimum value of VOH: 0.85 x
SIM_VDD
N/A
13
SIM_CLK
SIM card clock signal
I/O
Maximum value of VOL: 0.15 x
SIM_VDD
Minimum value of VOH: 0.85 x
SIM_VDD
N/A
14
SIM_VDD
SIM card power signal
O
1.8
N/A
15
RESET
Used to reset the NM1
module, which is active
at low level
I
N/A
N/A
16
NETLIGHT
Network status indication
O
N/A
N/A
17
RXD
Primary serial interface
that receives data
I
1.8
N/A
18
TXD
Primary serial interface
that transmits data
O
1.8
N/A
19
PSM_EINT
External interrupt
pin,
which is used to wake up
the NM1 module from
the PSM mode
I
N/A
N/A
20
SRCLKENAI
NFC interface
N/A
1.8
N/A

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Pin No.
Analog Signal
Definition
Pin Attribute
Input/
Output
Pin Voltage (V)
Remarks
21
USB_DP
USB+ signal
N/A
N/A
N/A
22
USB_DM
USB– signal
N/A
N/A
N/A
23
USB_EINT
USB_EINT
N/A
24
VIO18_EXT
1.8 V output power (In
PSM mode, no voltage is
output.)
O
Vmin = 1.53 V
Vnorm = 1.8 V
N/A
25
DVDD_IO
NC
NC
NC
N/A
26
NC
NC
N/A
N/A
N/A
27
GND
GND
N/A
N/A
N/A
28
UART1_RXD
Auxiliary serial interface
that receives data
I
1.8
N/A
29
UART1_TXD
Auxiliary serial interface
that transmits data
O
1.8
N/A
30
UART1_CTS
Determines whether data
is received.
N/A
1.8
N/A
31
UART1_RTS
Determines whether data
is transmitted.
N/A
1.8
N/A
32
I2C0_SDA
I2C0 data
I/O
N/A
N/A
33
I2C0_SCL
I2C0 clock
O
N/A
N/A
34
GND
GND
N/A
N/A
N/A
35
RF_ANT
RF antenna
Characteristic impedance of 50 ohms
36
GND
GND
N/A
N/A
N/A
37
GND
GND
N/A
N/A
N/A
38
RXD_DBG
Debugging serial
interface that receives
data
I
1.8
N/A
39
TXD_DBG
Debugging serial
interface that transmits
data
O
1.8
N/A
40
GND
GND
N/A
N/A
N/A
41
GND
GND
N/A
N/A
N/A
42
VSYS_BB
Input power
I
Vmin = 2.1 V
Vnorm = 3.3 V
Vmax = 3.63 V
N/A
43
VBAT_BOOST
Input power
I
Vmin = 2.1 V
Vnorm = 3.3 V
Vmax = 3.63 V
N/A

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Pin No.
Analog Signal
Definition
Pin Attribute
Input/
Output
Pin Voltage (V)
Remarks
44
VSYS_PA
Output power
O
3.3
N/A
45
GPIO11
Reserved
N/A
1.8
N/A
46
GPIO10
Reserved
N/A
1.8
N/A
47
GPIO25
Reserved
N/A
1.8
N/A
48
MD_WAKEUP
N/A
N/A
N/A
N/A
49
GPIO28
Reserved
N/A
1.8
N/A
50
AP_READY
N/A
N/A
N/A
N/A
51
STATUS
N/A
N/A
N/A
N/A
52
GPIO24
Reserved
N/A
1.8
N/A
53
GPIO34
Reserved
N/A
1.8
N/A
54
GPIO33
Reserved
N/A
1.8
N/A
55
GPIO21
Reserved
N/A
1.8
N/A
56
GPIO20
Reserved
N/A
1.8
N/A
57
GPIO8
Reserved
N/A
1.8
N/A
58
GPIO1
Reserved
N/A
1.8
N/A
59
GPIO19
Reserved
N/A
1.8
N/A
60
RTC_GPIO0
N/A
N/A
N/A
N/A
61
SIM_DET
GPIO35
N/A
SIM card detection
N/A
62
GPIO32
Reserved
N/A
1.8
N/A
63
AVDD33_VUSB
N/A
I
N/A
N/A
64
FREF
Base frequency
I
N/A
N/A
65
GPIO31
GPIO31
N/A
1.8
N/A
66
GND
GND
N/A
N/A
N/A

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3.2 Electrical Conditions
Table 3- 3 Electrical conditions
Signal
Description
Minimum
Value
Typical
Value
Maximum
Value
Unit
VBAT_BOOST
Input power
2.1
3.3
3.63
V
VSYS_BB
Input power
2.1
3.3
3.63
V
VSYS_PA
Output power
N/A
3.3
N/A
V
3.3 Power Interface
3.3.1 Power Pins and Grounding
The NM1 module can be powered by a battery or external power supply.
The GND signal pins indicate the power ground and signal ground of the NM1 module and need to be
connected to the ground of the PCB. Improper connections of the GND signal pins may have adverse impact on
the NM1 module performance.
3.3.2 Power Supply Requirements
The NM1 module's power design is important to its performance. The NM1 module can be powered by the
low-dropout regulator (LDO) with low static current and output current (up to 0.5 A) or the Li-MnO2 battery.
The input voltage range is from 2.1 V to 3.63 V. During data transmission, the power cannot be lower than the
minimum working voltage 2.1 V. Otherwise, errors will occur.
To ensure better power supply performance, it is recommended that three 47 µF (0805) ceramic capacitors and
100 nF, 100 pF, and 22 pF (0402) filter capacitors be connected in parallel at the VBAT input end of the module.
In addition, it is recommended that a TVS tube be connected to the VBAT input end to enhance the surge
voltage bearing capability of the module. In principle, a longer VBAT cable leads to a larger trace width. Figure
3- 2 shows the reference circuit.
Figure 3- 2 Power supply of the NM1 module

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3.4 SIM Card Interface
3.4.1 Pins
Table 3- 4 Definition and description of SIM card interface signals
Pin
No.
Signal Name
Signal Definition
Remarks
11
SIM_DATA
SIM card data pin
Voltage precision: 1.8 V±5%
Maximum current: about 60 mA
13
SIM_CLK
SIM card clock pin
12
SIM_RST
SIM card reset pin
14
SIM_VDD
SIM card power supply pin
3.4.2 SIM Card Interface Application
Figure 3- 3 SIM card interface application
To ensure a better external SIM card performance and prevent the external SIM card being damaged, design the
SIM card interface circuit in compliance with the following rules:
1. Place the external SIM card holder near the NM1 module. The external SIM card signal cable is 200 mm
or shorter and is away from the RF cable and VBAT power cable.
2. The SIM_VDD decoupling capacitance does not exceed 1 μF, and the capacitor is near the external SIM
card holder.
3. To prevent interference, keep the SIM_CLK and SIM_DATA signal cables at a certain distance from each
other and use a ground cable to separate them.
4. Connect the SIM_RST signal cable to the ground.
To ensure a better ESD performance, you are advised to use TVS tubes to protect the pins of the external SIM
card holder. The parasitic capacitance of the TVS tubes cannot be greater than 50 pF. Place ESD components
near the external SIM card holder. Route the external SIM card signal cable from the external SIM card holder
to the NM1 module through the ESD components.

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3.5 SPIs
3.5.1 Pins
Table 3-7 defines the SPI signals. (SPIs support the slave mode.)
Table 3- 5 SPI signal definition
Pin No.
Signal Name
Function Description
3
SPI_MISO
Master input and slave output
4
SPI_MOSI
Master output and slave input
5
SPI_ SCLK
SPI clock signal
6
SPI_CS
SPI selection signal
3.5.2 SPI Electrical Parameters and Application
The level of the SPI on the NM1 module is 1.8 V. If the host level is 3.3 V, add a level converter between the
NM1 module and host. The level converter that supports the SPI data rate is recommended. Figure 3- 4 shows
the reference circuit.
Figure 3- 4 Reference circuit
3.6 I2C Interface
3.6.1 Pins
Table 3- 6 I2C interface signal definition
Pin No.
Signal Name
Function Description
32
SDA
I2C serial data
33
SCL
I2C serial clock
I2C is a two-line bus for communication between ICs. It has a serial data cable (SDA) and a serial clock cable
(SCL) to transmit information between connected devices. I2C identifies each device based on its unique
address and can be used as both a transmitter and a receiver.

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3.6.2 I2C Interface Electrical Parameters and Application
Figure 3- 5 Reference circuit
3.7 UART Interface
3.7.1 Pins
The NM1 module provides three UART interfaces. The primary serial interface can be used for firmware
upgrade. The default baud rate is 115.2 kbit/s, and the downloading baud rate is 921.6 kbit/s. You can use a log
viewing tool to view logs over the debugging serial interface to debug software.
Table 3- 7 UART interface signal definition
Pin No.
Signal Name
Function Description
17
RXD
Data receiving over the primary serial interface
18
TXD
Data transmission over the primary serial
interface
28
UART1_RXD
Data receiving over the auxiliary serial interface
29
UART1_TXD
Data transmission over the auxiliary serial
interface
38
RXD_DBG
Data receiving over the debugging serial
interface
39
TXD_DBG
Data transmission over the debugging serial
interface
3.7.2 UART Interface Electrical Parameters and Application
Figure 3- 6 Reference circuit
The level of the UART interfaces on the NM1 module is 1.8 V. If the application system level is 3.3 V, add a
level converter to the connection between the NM1 module and application system over the serial interface.
Figure 3- 7 shows the reference circuit with a level converter, UM3202.

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Figure 3- 7 Reference circuit with a level converter
A triode can also be used for level conversion.
Figure 3- 8 Reference circuit with a triode for level conversion
Note: Connection methods of the debugging, auxiliary, and primary serial interfaces are similar.
3.8 USB Interface
3.8.1 Pins
The NM1 module has a USB 1.1 interface, which can only be used for module upgrade. If ESD design is
required, the maximum capacitance of ESD components must be less than 0.5 pF. Otherwise, waveform
distortion may occur, affecting bus communication. The differential impedance of differential data cables must
be within 90 ohms.
Table 3- 8 USB interface signal definition
Pin No.
Signal Name
Function Description
17
RXD
Receiving over the serial interface
18
TXD
Transmission over the serial interface
21
USB_DP
USB+ signal
22
USB_DM
USB– signal
63
AVDD33_VUSB
Internal USB power supply

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3.8.2 USB Interface Application
Figure 3- 9 Downloading interface application circuit
The nominated input power of the NM1 module is 3.3 V. When the USB interface is used for downloading, add
an LDO circuit to keep the circuit voltage at 3.3 V.
3.9 Power-On/Power-Off and Reset Interface
3.9.1 PWRKEY Pin
Table 3- 9 PWRKEY signal definition
Pin No.
Signal Name
Function Description
7
PWRKEY
NM1 module power-on
3.9.2 Power-On/Power-Off Interface Application
To power on the NM1 module, lower the PWRKEY pin to a low level for a period of time and then disconnect it
or raise it to a high level.
Figure 3- 10 PWRKEY interface application circuit