Introduction to ARM7 Based Microcontroller (LPC2148)

Increasingly, embedded systems developers and system-on-chip designers select specificmicroprocessor cores and a family of tools, libraries, and off-the-shelf components toquickly develop new microprocessor-based products and applications. ARM is one of the major options available for embedded system developer.

Over the last few years, the ARM architecture has become the most pervasive 32-bitarchitecture in the world, with wide range of ICs available from various IC manufacturers. ARM processors are embedded in products ranging from cell/mobilephones to automotive braking systems. A worldwide community of ARM partners andthird-party vendors has developed among semiconductor and product design companies,including hardware engineers, system designers, and software developers.

ARM7 is one of the widely used micro-controller family in embedded system application. This section is humble effort for explaining basic features of ARM-7.

ARM is a family of instruction set architectures for computer processors based on a reduced instruction set computing (RISC) architecture developed by British company ARM Holdings.
A RISC-based computer design approach means ARM processors require significantly fewer transistors than typical processors in average computers. This approach reduces costs, heat and power use. These are desirable traits for light, portable, battery-powered devices—including smartphones, laptops, tablet and notepad computers), and other embedded systems. A simpler design facilitates more efficient multi-core CPUs and higher core counts at lower cost, providing higher processing power and improved energy efficiency for servers and supercomputers.

SOME FACTS YOU MUST KNOW
In 2005, about 98% of all mobile phones sold used at least one ARM processor. The low power consumption of ARM processors has made them very popular: 37 billion ARM processors have been produced as of 2013, up from 10 billion in 2008. The ARM architecture (32-bit) is the most widely used architecture in mobile devices, and most popular 32-bit one in embedded systems.
According to ARM Holdings, in 2010 alone, producers of chips based on ARM architectures reported shipments of 6.1 billion ARM Based processors, representing 95% of smartphones, 35% of digital televisions and set-top boxes and 10% of mobile computers. It is the most widely used 32-bit instruction set architecture in terms of quantity produced.

LET’S START WITH LPC 2148
LPC2148 is the widely used IC from ARM-7 family. It is manufactured by Philips and it is pre-loaded with many inbuilt peripherals making it more efficient and a reliable option for the beginners as well as high end application developer.

Let us go through the features of LPC214x series controllers.

• 8 to 40 kB of on-chip static RAM and 32 to 512 kB of on-chip flash program memory.128 bit wide interface/accelerator enables high speed 60 MHz operation.
• In-System/In-Application Programming (ISP/IAP) via on-chip boot-loader software.Single flash sector or full chip erase in 400 ms and programming of 256 bytes in 1ms.
• EmbeddedICE RT and Embedded Trace interfaces offer real-time debugging with theon-chip RealMonitor software and high speed tracing of instruction execution.
• USB 2.0 Full Speed compliant Device Controller with 2 kB of endpoint RAM.In addition, the LPC2146/8 provides 8 kB of on-chip RAM accessible to USB by DMA.
• One or two (LPC2141/2 vs. LPC2144/6/8) 10-bit A/D converters provide a total of 6/14analog inputs, with conversion times as low as 2.44 us per channel.
• Single 10-bit D/A converter provides variable analog output.
• Two 32-bit timers/external event counters (with four capture and four comparechannels each), PWM unit (six outputs) and watchdog.
• Low power real-time clock with independent power and dedicated 32 kHz clock input.
• Multiple serial interfaces including two UARTs (16C550), two Fast I2C-bus(400 kbit/s), SPI and SSP with buffering and variable data length capabilities.
• Vectored interrupt controller with configurable priorities and vector addresses.
• Up to 45 of 5 V tolerant fast general purpose I/O pins in a tiny LQFP64 package.
• Up to nine edge or level sensitive external interrupt pins available.
• On-chip integrated oscillator operates with an external crystal in range from 1 MHz to30 MHz and with an external oscillator up to 50 MHz.
• Power saving modes include Idle and Power-down.
• Individual enable/disable of peripheral functions as well as peripheral clock scaling foradditional power optimization.
• Processor wake-up from Power-down mode via external interrupt, USB, Brown-OutDetect (BOD) or Real-Time Clock (RTC).
• Single power supply chip with Power-On Reset (POR) and BOD circuits:
– CPU operating voltage range of 3.0 V to 3.6 V (3.3 V ± 10 %) with 5 V tolerant I/Opads.

^{* adopted from datasheet of LPC 2148. Each inbuilt peripheral will be explained in brief later on.}

The list of feature is enough to explain why it has covered such a huge market for high end applications such as mobile phones, tablets etc.

FIRST STEP- HARDWARE REQUIREMENT

Here is the pin configuration of LPC 2148.

Now let us start with the hardware requirement of LPC2148.
LPC2148 need minimum below listed hardware to work properly.

1.                  Power Supply
2.                  Crystal Oscillator
3.                  Reset Circuit
4.                  RTC crystal oscillator (This is not necessary if you are not using RTC. However this is considered as necessary requirement)
5.                  UART

1. Power Supply
LPC2148 works on 3.3 V power supply. LM 117 can be used for generating 3.3 V supply. However, basic peripherals like LCD, ULN 2003 (Motor Driver IC) etc. works on 5V. So AC mains supply is converted into 5V using below mentioned circuit and after that LM 117 is used to convert 5V into 3.3V.


Block diagram for power supply is given below.
         
Transformer:It is used to step down 230V AC to 9V AC supply and provides isolation between power grids and circuit.

Rectifier: It is used to convert AC supply into DC.

Filter:It is used to reduce ripple factor of DC output available from rectifier end.

Regulator:It is used to regulate DC supply output.
Circuit for this is as shown below.


Here, Regulator IC 7805 is used to provide fix 5V dc supply.

Now we can use LM 117 for generating 3.3V supply from 5V using below circuit.

Calculations

2. Reset Circuit

Reset button is essential in a system to avoid programming pitfalls and sometimes to manually bring back the system to the initialization mode. Circuit diagram for reset is as shown below.

MCP 130T is a special IC used for providing stable RESET signal to LPC 2148.


3. Oscillator Circuit
Oscillations, the heartbeat, are provided using a crystal and are necessary for the system to work.


The value of capacitors C20 & C21 depends upon the frequency of crystal Y3. General circuit and its equivalent circuit is as shown below.


Recommended values are as shown in table.


We can also use external oscillator for providing system clock. Circuit for this application is as given below.

4. RTC Oscillator Circuit
It provides clock for RTC operation.


5. UART
LPC 2148 has inbuilt ISP which means we can program it within the system using serial communication on COM0. It has also COM1 for serial communication. MAX 232/233 IC must be used for voltage logic conversion. Related connections are as given below.


Once above listed circuit design is ready, we are ready to go further.

What is Power Line Communication?

Different communication technologies are being used for the transmission of information from one end to another depending on the feasibility and needs. Some include Ethernet cables, fiber optics, wireless transmission, satellite transmission, etc. A vast amount of information travels through the entire earth every day and it creates an essential need for a transmission medium that is not only fast but economically reasonable as well. One of the technologies that fit in the above stated criteria is PLCC.

PLCC, Power Line Carrier Communication, is an approach to utilize the existing power lines for the transmission of information. In today’s world every house and building has properly installed electricity lines. By using the existing AC power lines as a medium to transfer the information, it becomes easy to connect the houses with a high speed network access point without installing new wirings.

This technology has been in wide use since 1950 and was mainly used by the grid stations to transmit information at high speed. Now a days this technology is finding wide use in building/home automation as it avoids the need of extra wiring. The data collected from different sensors is transmitted on these power lines thereby also reducing the maintenance cost of the additional wiring. In some countries this technology is also used to provide Internet connection.

History

The idea of using an existing medium to send the communication signals is as old as the telegraph itself. But it had not been possible until the recent decades. The first significant step in the field was when two patents were issued to American Telephone and Telegraph Company in the name of 'Carrier Transmission over Power Circuits' in 1920. After four years later in 1924 two other patents were filed for the systems transmitting and receiving communication signals over three phase power lines.

Harsh characteristics of the power cables were the key problem in further development. Researchers were involved to overcome the unpredictable characteristics of the power lines. Since the early 1980, spread spectrum power line communication was the main focus of the research. This technology is now developed far better than that initial improvement and is promising a reliable utilization in home automation and security systems.

Applications of PLCC

PLCC technology can be deployed into different types of applications in order to provide economic networking solutions. Hence merging with other technologies it proves useful in different areas. These are few key areas where PLC communications are utilized:

a.       Transmission & Distribution Network: PLCC was first adopted in the electrical transmission and distribution system to transmit information at a fast rate.

b.      Home control and Automation: PLCC technology is used in home control and automation. This technology can reduce the resources as well as efforts for activities like power management, energy conservation, etc.

c.       Entertainment: PLCC is used to distribute the multimedia content throughout the home.

d.      Telecommunication: Data transmission for different types of communications like telephonic communication, audio, video communication can be made with the use of PLCC technology.

e.       Security Systems: In monitoring houses or businesses through surveillance cameras, PLCC technology is far useful.

f.       Automatic Meter Reading – Automatic Meter reading applications use the PLCC technology to send the data from home meters to Host Central Station.

Power Line Communications

The smart grid implements two-way communication channels over existing power distribution networks. Modern networks might be comprised of a variety of new alternative energy sources. These sources include solar and wind power as well as new types of electric appliances, such as smart appliances and electric vehicles. In many parts of the world, narrowband power line communications (PLC) technology has proven to be a robust and cost-optimized solution in large deployments of smart meters.
Atmel® offers PLC solutions designed specifically for narrowband communications using the low-voltage electric grid. Drawing on our deep expertise in PLC modem technology and extensive collaboration with utilities and metering OEMs, we’ve created solutions offering an unprecedented level of integration and performance. Our solutions support various modulation schemes including G3-PLC and PRIME (PoweRline Intelligent Metering Evolution) Thanks to the communications software provided by our solution, the management of PLC networks turns into a transparent process. Users can focus on top-level applications and access the Atmel® PLC software stack via user-friendly application programming interfaces (APIs).

Key Features

• Best-in-class sensitivity and high-temperature stability.
• Improved analog front end (AFE) providing outstanding efficiency.
• Price-competitive, high-performance solutions.
• Free software stacks for PLC

Power Line Communication (PLC) is a communication technology that enables sending data over existing power cables. This means that, with just power cables running to an electronic device (for example) one can both power it up and at the same time control/retrieve data from it in a half-duplex manner.

PLC Market: Overview

Segments
For the purpose of understanding, PLC can be broadly viewed as:

1. Narrowband PLC
2. Broadband PLC

Narrowband PLC works at lower frequencies (3-500 kHz), lower data rates (up to 100s of kbps), and has longer range (up to several kilometers), which can be extended using repeaters. Broadband PLC works at higher frequencies (1.8-250 MHz), high data rates (up to 100s of Mbps) and is used in shorter-range applications.

Recently, narrowband Power Line Communication has been receiving widespread attention due to its applications in the Smart Grid. Another application that narrowband PLC has been used in is smart energy generation, particularly in micro-inverters for solar panels.

Broadband PLC, in contrast, has mainly found acceptance as a last-mile solution for Internet distribution and home networking. With its high data rates and no additional wiring, broadband PLC is seen as an exciting and effective technology for multimedia distribution within homes. This optimism in the market is reflected by the recent acquisitions of Intellon by Atheros, Coppergate by Sigma, DS2 by Marvell, and Gigle by Broadcom, all in the Home Area Networking (HAN) segment.

There is another way to classify Power Line Communication and that is:

1. PLC over AC lines
2. PLC over DC lines

While most companies are currently geared towards providing AC-PLC solutions, PLC in DC lines also has applications. Two such applications are PLC over the DC-bus in distributed energy generation, and PLC in transportation (electronic controls in airplanes, automobiles and trains). This use reduces wiring complexity, weight, and ultimately cost of communications inside vehicles. However, in this article, we will be dealing mostly with narrowband PLC over AC lines.

Competition
The narrowband PLC market is seeing healthy competition, with a large number of PLC suppliers joining the fray, including:

1.  Cypress Semiconductor
2.  Echelon
3.  ST Microelectronics
4.  Yitran
5.  Texas Instruments
6.  Maxim
7.  Semitech Semiconductor
8.  Ariane Controls
9.  ADD Semiconductor
10.  Microchip

Companies in the broadband PLC segment include:
1.  Atheros
2.  Sigma
3.  Marvell
4.  Broadcom
5.  Lantiq
6.  Maxim
7.  Plugtek

PLC Technology: How does it work?
PLC is like any other communication technology whereby a sender modulates the data to be sent, injects it onto medium, and the receiver de-modulates the data to read it. The major difference is that PLC does not need extra cabling, it re-uses existing wiring. Considering the pervasiveness of power lines, this means with PLC, virtually all line- powered devices can be controlled or monitored!

When discussing communication technology, it is often useful to refer to the 7-layer OSI model. Some PLC chips can implement only the Physical Layer of the OSI model, while others integrate all seven layers. One could use a Digital Signal Processor (DSP) with a pure software realization of the MAC and an external PHY circuit, or an optimized System-on-Chip (SoC) solution, which includes the complete PLC – MAC and PHY. The Cypress CY8CPLCXX series is an example of the latter, with a ready-to-use Physical and Network layer, and a user-programmable application layer. Before moving on to the applications of PLC, let’s first understand the various aspects of the Physical layer by viewing it as three segments on the basis of data rate.

Modulation Schemes
A variety of modulation schemes can be used in PLC. Some of these are Orthogonal Frequency Division Multiplexing (OFDM), Binary Phase Shift Keying (BPSK), Frequency Shift Keying (FSK), Spread-FSK (S-FSK) and proprietary schemes too (for example Differential Code Shift Keying (DCSK) from Yitran). In the table below, BPSK, FSK, SFSK and OFDM are compared on the basis of two important criteria – bandwidth efficiency and complexity (cost).


OFDM in particular offers high data rates, but requires computational horsepower to churn out Fast Fourier Transforms (FFT) and Inverse-FFT (IFFT), as required by the scheme. On the other hand, BPSK, FSK are robust and simple but offer lower data rates. The current trend is to move towards OFDM with PSK modulation (G3 and probably P1901.2). Such heavy computation will require DSP capability, whereas FSK, PSK and SFSK can be accomplished by a microcontroller.

Standards
Various standards have been developed in order to ensure reliable communications and inter-operability, especially for the smart grid and home networking. Examples of such standards are:


These, along with the organizations that govern them like CENELEC, FCC, ARIB, Homeplug Power Alliance specify ranges for operation of PLC. If a worldwide standard for PLC were to be established, this would have a positive impact on adoption of PLC. So far, the G3-PLC standard is touted as the most robust scheme available, and the IEEE 1901.2 working group is committed to developing a universally acceptable standard.

Frequencies
Different regions of the world have different frequency bands allocated to narrowband PLC. The table below summarizes the different frequencies available for narrowband PLC communication in the respective region.

Where:
CENELEC - European Committee for Electrotechnical Standardization.
ARIB – Association of Radio Industries & Businesses
EPRI – Electric Power Research Institute
FCC – Federal Communications Commission

APPLICATIONS
Earlier, we saw that PLC is widely used in the Smart Grid and in micro-inverters. As the market gets familiar with this technology, PLC should see wider adoption in other applications like lighting (e.g. traffic light control, LED dimming), industrial (e.g. UPS communicating to a network device, irrigation control), machine-to-machine (e.g. vending machines, a hotel’s reception-to-room communication), telemetry (e.g. offshore oil rigs), transport (e.g. Electronics in cars, trains and airplanes) and indeed, applications of PLC are only limited by one’s creativity. In this article, we will find out a little more about PLC in energy generation and conservation markets.