当智能电表在电力系统中正如火如荼的大发展时，水表也在朝向智能化、全电子的方向快速发展。一方面因为全球水资源的短缺迫使政府重视节水和水量控制，另一方面也源于现代工业技术的发展成熟使得智能水表的实现成为可能。

　　水表技术的创新发展是实现用水智能测量的重要武器。超声波水表是采用超声波时差原理，采用工业级电子元器件制造而成的全电子水表。利用一对超声波换能器相向交替(或同时)收发超声波，通过检测超声波在介质中的顺流和逆流传播时间差来间接测量流体的流速，再通过流速来计算流量的这种间接测量方法—超声波测量，使智能水表变为现实。

　　图1：超声波时差法测量原理示意图

　　与传统机械式水表相比较，精度高、可靠性好、量程比宽、寿命长、无活动部件、任意角度安装、更换非常灵活等都是超声波水表所具有的重要优势：

　　• 精度高：测量的分辨率高，识别非常小流量;

　　• 可靠性好：超声波回波测量更加稳定可靠;

　　• 量程比宽：始动流量非常小(< 2 L/h)，微小变化可以获知;

　　• 寿命长：尽管测量速度很快，但还是可以拥有非常长的使用寿命;

　　• 无活动部件：不影响流体特性，测量性能更加优越;

　　• 更换非常灵活：更换非常简单，无需断管网。

　　低功耗MCU助力超声波水表突破功耗瓶颈

　　电子智能水表应用中功耗至关重要的问题，水表应用的标准要求水表的电池至少6年不能更换，这对整个系统的功耗提出了苛刻的要求，也是一直制约着超声波水表发展的原因。下图为低功耗超声波水表方案的系统框图，主要由TDC-GP30和EFM32TG840组成。

　　图2：低功耗超声波水表方案的系统框图

【EFM32TG】

EFM32TG Reference Manual

• 32-bit ARM Cortex-M3 processor running at up to 32 MHz

• Up to 32 kB Flash and 4 kB RAM memory

• Energy efficient and autonomous peripherals

• Ultra low power Energy Modes with sub-µA operation

• Fast wake-up time of only 2 µs

The EFM32TG microcontroller series revolutionizes the 8- to 32-bit market with acombination of unmatched performance and ultra low power consumption in bothactive- and sleep modes. EFM32TG devices consume as little as 150 µA/MHz in run mode, and as little as 1.0 µA with a Real Time Counter running, Brown-out and full RAM and register retention.

EFM32TG's low energy consumption outperforms any other available 8-, 16-, and 32-bit solution. The EFM32TG includes autonomous and energy efficient peripherals, high overall chip- and analog integration, and the performance of the industry standard 32-bit ARM Cortex-M3 processor.

Energy Friendly Microcontrollers

1.1 Typical Applications

The EFM32TG Tiny Gecko is the ideal choice for demanding 8-, 16-, and 32-bit energy sensitive applications. These devices are developed to minimize the energy consumption by lowering both the power and the active time, over all phases of MCU operation. This unique combination of ultra low energy consumption and the performance of the 32-bit ARM Cortex-M3 processor, help designers get more out of the available energy in a variety of applications.

Ultra low energy EFM32TG microcontrollers are perfect for:

• Gas metering

• Energy metering

• Water metering

• Smart metering

• Alarm and security systems

• Health and fitness applications

• Industrial and home automation

0 1 2 3 4

1.2 EFM32TG Development

Because EFM32TG use the Cortex-M3 CPU, embedded designers benefit from the largest development ecosystem in the industry, the ARM ecosystem. The development suite spans the whole design process and includes powerful debug tools, and some of the world’s top brand compilers. Libraries withdocumentation and user examples shorten time from idea to market.

The range of EFM32TG devices ensure easy migration and feature upgrade possibilities.

2 About This Document

This document contains reference material for the EFM32TG series of microcontrollers. All modules andperipherals in the EFM32TG series devices are described in general terms. Not all modules are present in all devices, and the feature set for each device might vary. Such differences, including pin-out, are covered in the device-specific datasheets.

2.1 Conventions

Register Names

Register names are given as a module name prefix followed by the short register name:

TIMERn_CTRL - Control Register

The "n" denotes the numeric instance for modules that might have more than one instance.

Some registers are grouped which leads to a group name following the module prefix:

GPIO_Px_DOUT - Port Data Out Register,

where x denotes the port instance (A,B,...).

Bit Fields

Registers contain one or more bit fields which can be 1 to 32 bits wide. Multi-bit fields are denoted with

(x:y), where x is the start bit and y is the end bit.

Address

The address for each register can be found by adding the base address of the module (found in the

Memory Map), and the offset address for the register (found in module Register Map).

Access Type

The register access types used in the register descriptions are explained in Table 2.1 (p. 3)

EFM32TG840 DATASHEET

• ARM Cortex-M3 CPU platform

• High Performance 32-bit processor @ up to 32 MHz

• Wake-up Interrupt Controller

• Flexible Energy Management System

• 20 nA @ 3 V Shutoff Mode

• 0.6 µA @ 3 V Stop Mode, including Power-on Reset, Brown-out Detector, RAM and CPU retention

• 1.0 µA @ 3 V Deep Sleep Mode, including RTC with 32.768 kHz oscillator, Power-on Reset, Brown-out Detector, RAM and CPU retention

• 51 µA/MHz @ 3 V Sleep Mode

• 150 µA/MHz @ 3 V Run Mode, with code executed from flash

• 32/16/8 KB Flash

• 4/4/2 KB RAM

• 56 General Purpose I/O pins

• Configurable push-pull, open-drain, pull-up/down, input filter, drive strength

• Configurable peripheral I/O locations

• 16 asynchronous external interrupts

• Output state retention and wake-up from Shutoff Mode

• 8 Channel DMA Controller

• 8 Channel Peripheral Reflex System (PRS) for autonomous inter-peripheral signaling

• Hardware AES with 128/256-bit keys in 54/75 cycles

• Timers/Counters

• 2× 16-bit Timer/Counter

• 2×3 Compare/Capture/PWM channels

• 16-bit Low Energy Timer

• 1× 24-bit Real-Time Counter

• 1× 16-bit Pulse Counter

• Watchdog Timer with dedicated RC oscillator @ 50 nA

• Integrated LCD Controller for up to 8×20 segments

• Voltage boost, adjustable contrast and autonomous animatio

• Communication interfaces

• 2× Universal Synchronous/Asynchronous Receiver/Transmitter

• UART/SPI/SmartCard (ISO 7816)/IrDA/I2S

• Triple buffered full/half-duplex operation

• Low Energy UART

• Autonomous operation with DMA in Deep Sleep Mode

• I2C Interface with SMBus support

• Address recognition in Stop Mode

• Ultra low power precision analog peripherals

• 12-bit 1 Msamples/s Analog to Digital Converter

• 8 single ended channels/4 differential channels

• On-chip temperature sensor

• 12-bit 500 ksamples/s Digital to Analog Converter

• 2 single ended channels/1 differential channel

• 2× Analog Comparator

• Capacitive sensing with up to 8 inputs

• 3× Operational Amplifier

• 6.1 MHz GBW, Rail-to-rail, Programmable Gain

• Supply Voltage Comparator

• Low Energy Sensor Interface (LESENSE)

• Autonomous sensor monitoring in Deep Sleep Mode

• Wide range of sensors supported, including LC sensors and capacitive buttons

• Ultra efficient Power-on Reset and Brown-Out Detector

• 2-pin Serial Wire Debug interface

• 1-pin Serial Wire Viewer

• Pre-Programmed UART Bootloader

• Temperature range -40 to 85 ºC

• Single power supply 1.98 to 3.8 V

• QFN64 package 32-bit ARM Cortex-M0+, Cortex-M3 and Cortex-M4 microcontrollers for:

• Energy, gas, water and smart metering

• Health and fitness applications

• Smart accessories

• Alarm and security systems

• Industrial and home automation

EFM32TG840系列

EFM32TG840F8-QFN64

EFM32TG840F16-QFN64

EFM32TG840F32-QFN64

【TDC-GP30】

TDC-GP30 Ultrasonic Flow Converter

Features

High performance and ultra-low power 32-Bit CPU with 4k NVRAM and 4k ROM Up to 31 multi-hits for flow measurement yield the highest accuracy

Advanced high-precision analog part

Transducers can be connected directly to GP30, no external components required

Amplitude measurements of receiving signal for secure bubble, aging and empty spool piece detection

High update rates with very low power consumption (e.g. 6 µA@8Hz)

Benefits

Lowest power solution for ultrasonic water meters

On-chip firmware allows fastest time-to-market

Best measurement performance for leakage detection

Product parameters

Analog Frontend ：Yes

First Wave Detection ： Yes

Amplitude Measurement ： Yes

Number of Hits ： 31

Resolution [ps] ：11

Operating Supply Range ： 2.5 to 3.6

Interface ： SPI, UART, Pulse

CPU ： 32-bit

Firmware

Memory ： 4k NVRAM, 4k ROM

GPIO ：6

Ambient Temperature Range [°C] ： -40 to +125

Package ： QFN32, QFN40

　　由于系统中控制器通常是耗电大户，所以要降低整个系统的功耗，超低功耗的MCU是必需的。Cortex M3相对ARM7来说性能相当，但功耗低很多，灵活性也大，特别适合电池供电的产品开发，也被业界普遍认为是用于替换8位MCU市场的首选32位MCU。Silicon Lab的EFM32TG系列是基于Cortex M3内核的堪称业界最高能效MCU芯片，其独有的LESENSE低功耗传感器接口和PRS外围反射系统使得设计很灵活，带有低功耗的LCD接口，封装也很小，特别适合低功耗表计和各类LCD手持/便携终端设备。EFM32TG840内部框图如下：

　　图3：EFM32TG840内部框图

　　EFM32系列单片机通过许多关键性创新来降低功耗。例如PRS系统，可以在MCU睡眠的情况下，外设与外设之间自主进行交流和工作，低功耗LETIMER及LEUART，可以在深度睡眠模式下工作。与其他32位MCU相比，其集成的高效率DC-DC转换器可以实现系统功耗降低40%，电池寿命提高60%!其休眠模式下功耗比同类竞争对手低5-10倍(最低休眠电流可低至20nA)，工作模式下功耗比同类竞争对手低33%。

　　增强型直接存储器存取(DMA)可以降低90%协议相关功耗，RAM和寄存器保持状态能够在2μs内快速唤醒。该系列MCU产品还具有专利技术LCD控制器，其电荷再分配架构能够在不影响性能的情况下降低约40%显示器功耗。正是EFM32TG840的这些低功耗特性才使得超声波水表的电池能够8年不用更换成为可能。

　　除了低功耗水表专用的MCU，世强还可以提供业内先进的超声波流量测量芯片。

　　简化超声波水表设计的新一代超声波流量仪

　　TDC-GP30是超声波流量测量新的一步，它大大简化了超声波和热水仪的设计，而且对于节省能源的新一代的超声波流量仪表是非常重要的。弱电性能容许标准的2/3AA或者AA锂亚硫酰氯电池保持6-8HZ的频率下使用，即使在水表中也可以使用。TDC-GP30是容许你在一片IC上执行所有测量任务的系统芯片。

　　TDC-GP30功能特点如下：

　　• 非常容易适应超声波和热水仪的二芯片解决方案

　　• 单个芯片适用于很多工业应用或者纯流量应用部分

　　• 所有的流量和温度运算已经由GP30完成

　　• 外接的up仅仅用于表面的接口和其他一些通用的任务

　　• 综合的标准的脉冲式接口使以热量和水流量仪表为基础的TDC-GP30替代了一对一的机械流量仪表

　　图4：TDC-GP30产品框图

　　相关元件供应

　　型号：EFM32TG840F32-QFN64品牌： SILICON LABS

　　型号：TDC-GP30-F01 品牌：AMS

　　型号：EFM32TG840F32-QFN64T 品牌：SILICON LABS

      【超声波水表】

　　超声波水表是通过检测超声波声束在水中顺流逆流传播时因速度发生变化而产生的时差，分析处理得出水的流速从而进一步计算出水的流量的一种新式水表。

　　特点:始动流速低，量程比宽，测量精度高工作稳定。

　　内部无活动部件无阻流元件，不受水中杂质的影响，使用寿命长。输出通讯功能齐全，满足各类通讯和无线组网要求。

　　具有优秀的小流量检测能力，能解决众多传统水表的问题，更加适合水费梯度收费，更加适合水资源的节约和合理利用，具有广阔的市场和使用前景。

　　超声波水表是采用超声波时差原理，采用工业级电子元器件制造而成的全电子水表。与机械式水表相比较具有精度高，可靠性好，量程比宽，使用寿命长，无任何活动部件，无需设置参数，任意角度安装等特点。

　　1、工业过程计量与控制

　　2、替代机械式流量计以提高计量可靠性。

　　3、替代各类高性能流量计。