ARM Processor Based Embedded System for Remote Data Acquisition

Copyright © 2014 IJECCE, All right reserved 8

International Journal of Electronics Communication and Computer Engineering Volume 5, Issue 1, ISSN (Online): 2249_–071X, ISSN (Print): 2278_–4209

ARM Processor Based Embedded System for Remote

Data Acquisition

Raj Kumar Tiwari

Email: rktiwari2323@yahoo.co.in

Santosh Kumar Agrahari

Dept. of Electronics & Instrumentation Engineering, Hindustan College of Science & Technology, Mathura, UP, India

Email: santosh.agrahari.hcst@sgei.org

Abstract - The embedded systems are widely used for the

data acquisition. The data acquired may be used for monitoring various activity of the system or it can be used to control the parts of the system. Accessing various signals with remote location has greater advantage for multisite operation or unmanned systems. The remote data acquisition used in this paper is based on ARM processor. The Cortex M3 processor used in this system has in-built Ethernet controller which facilitate to acquire the remote data using internet. The system developed provides high performance, low power consumption, smaller size & high speed.

Keywords–ARM Processor, Cortex M3, Data Acquisition,

Embedded System, LM3S8962, Remote Sensing.

I. I

ARM processors are found in numerous market segments, including networking, automotive, mobile and consumer electronics. Within each segment ARM processors can be found in multiple applications. The uses of ARM processor is rapidly growing due to cost sensitive and high volume production [1, 2, 3]. In some of applications, it is required to access the data from remote locations. Due to which an embedded system has to acquire these data with some means of communication. To access the remote data various methods are used. One of them is to use internet to access these data [4, 5].

Embedded systems are used to acquire various data (signals) & have to control the system designed for an application. These systems can read signals like temperature, pressure or any other physical parameters. Accessing remote data are useful in an unmanned system or multisite operation. The internet will help to acquire such data. To access remote data, internet will be medium to provide a command through web browser [6, 7, 8]. The data has to be accessed in real time, so the interface used in embedded system must be efficient & fast to acquire data. The features of ARM processor Cortex M3 have enhanced capability in terms of operating frequency, size, performance, code density etc [9, 10, 13]. Thus in this paper we will provide a remote data acquisition system based on Cortex M3 ARM processor.

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An embedded system consists of a processor along with various peripheral devices and signal conditioning circuits to acquire data. The sensors and transducers selection depends upon the application for which various parameters have to be measured. Each of the sensors is connected with signal conditioning circuitry. Then these signals are

connected with the peripherals of the processor like digital input/output (I/O), analog to digital converter (ADC) etc. The processor having sufficient general purpose input output (GPIO) pins must be selected to provide interface with these signals. The processor selection is the core task for developing any embedded system. The 32-bit ARM processor is the first choice nowadays due to its high performance, low power consumption, high efficiency, high code density etc. In the family of ARM processor, Cortex M3 microcontroller provides optimized features which are best suitable for the most of the embedded systems [11, 12]. Further to acquire the data remotely, a communication medium of internet is used through web browser. To connect with the internet, an Ethernet interface is required as shown in fig 1.

Fig.1. Remote data acquisition system

III. ARM P

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The ARM Cortex M3 processors provide a high-performance, low-cost platform that meets the system requirements of minimal memory implementation, reduced pin count and low power consumption, while delivering outstanding computational performance and exceptional system response to interrupts. The features of Cortex M3 processor includes compact core, thumb-2 instruction set for mixed 16 & 32 bit operation, rapid application execution through Harvard architecture characterized by separate buses for instruction and data, better performance and power efficiency [13, 14].

Copyright © 2014 IJECCE, All right reserved 9

International Journal of Electronics Communication and Computer Engineering Volume 5, Issue 1, ISSN (Online): 2249_–071X, ISSN (Print): 2278_–4209

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The various signals are analog and digital in nature. Depending on the type of signals to be acquired by the system, many sensors and transducers are used. For example to acquire temperature various transducers can be used like thermocouple, RTD, thermister while for pressure measurements strain gauge, piezo-electric sensors can be used. These sensors and transducers used to acquire signals provide very low voltages. We need to use instrumentation amplifier circuit (Fig. 2) or any other form of signal conditioning circuitry so that the input signals may be processed further by the processor suitably.

Fig.2. Instrumentation amplifier

V. I

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To access the various data from remote location the internet is the easiest method. To interface this communication with the embedded system an Ethernet controller is required. The LM3S8962 microcontroller has in-built Ethernet interface on chip. The Stellaris Ethernet controller consists of a fully integrated media access controller (MAC) and network physical (PHY) interface. The Ethernet controller conforms to IEEE 802.3 specifications and fully supports 10BASE-T and 100BASE-TX standards. It has multiple operational modes: full and half duplex 10/100 Mbps, power saving and power down mode, programmable MAC address, physical media manipulation, automatic MDI/MDI-X cross-over correction [14, 15, 16].

As shown in fig. 3, the Ethernet controller is functionally divided into two layers: the media access controller (MAC) layer and the network physical (PHY) layer. The CPU accesses the Ethernet controller via the MAC layer. The MAC layer provides transmits and receives processing for Ethernet frames. The MAC layer also provides the interface to the PHY layer via an internal media independent interface (MII). The PHY layer communicates with the Ethernet bus.

Fig.3. Ethernet controller

The Ethernet data is carried by Ethernet frame. The basic frame format is shown in fig. 4. The seven fields of the frame are transmitted from left to right. The bits within the frame are transmitted from least significant bit to most significant bits.

Fig.4. Ethernet frame

The Preamble field is used to synchronize with the received frame’s timing.

The start frame delimiter (SFD) field follows the preamble pattern and indicates the start of the frame. Its value is 1010.1011.

The destination address field specifies for which the frame is intended.

The source address field identifies the station from which the frame was initiated.

The length/type field indicates the maximum length of data less than or equal to 1500 while it indicates type for greater or equal to 1536.

The data field is a sequence of octets that is at least 46 in length, up to 1500 in length.

The frame check sequence (FRC) carries the cyclic redundancy check (CRC) value.

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The hardware configuration required to interface Ethernet controller is shown in fig. 5. The Ethernet controller is connected with isolation transformer to the PHY layer. The isolation transformers are various types like low profile package, isolation transformer with integrated RJ45 connector etc.

Fig.5. Interface to an Ethernet jack (RJ45)

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Copyright © 2014 IJECCE, All right reserved 10

International Journal of Electronics Communication and Computer Engineering Volume 5, Issue 1, ISSN (Online): 2249_–071X, ISSN (Print): 2278_–4209

register, Ethernet MAC receive control register, Ethernet MAC number of packet register, Ethernet MAC management control register etc. Some other registers are also required to initialize for PHY layer like Ethernet PHY management register for control, status, PHY identifier, auto negotiation advertisement, diagnostic, transceiver control, LED configuration etc.

Fig. 6 Hyper text transfer protocol

Once the Ethernet controller is initialized in desired mode of operation, a web browser can send or receive data frame using hyper text transfer protocol (HTTP). HTTP is the basis of realizing TCP/IP model, as shown if fig. 6, which has five layers: Application layer uses HTTP, transport layer uses TCP, network/internet layer uses IP, data link layer uses Ethernet and physical layer uses Ethernet PHY.

VIII. R

The use of cortex M3 processor having in-built Ethernet controller for remote data acquisition system has been compared with various other systems developed earlier for data acquisition on internet. One of the systems used based on 8051 microcontroller with external Ethernet controller CS8900A and other is the ARM9 processor with external Ethernet controller RTL8019AS. Here some of the parameters compared are listed in table 1 as follows: Table 1: Comparison of various parameters

Processor used Size Power Consumption Performance Speed

8051 microcontroller with external Ethernet controller CS8900A

100% 5V/50mA

In few watts

Slower 24 MHz

ARM9 processor with external Ethernet controller RTL8019AS

70% 3.3V/5mA

In ~100mWatts

Moderate 50 MHz

Cortex M3 with in-built Ethernet controller

50% 3.3V/2mA

In <50mWatts

Faster 80 MHz

Therefore, from the table shown above we see that the system based on 8051 microcontrollers were larger in size, more power consuming and slower performance. The ARM9 processor with external Ethernet controller has moderate size, power consumption and performance. The optimum system can be developed using Cortex M3 processor with in-built Ethernet controller having smaller in size and less power hungry while faster performance.

IX. C

The ARM processor based embedded system for remote data acquisition provides high performance, low power consumption, small size, and high speed of operation. Varieties of embedded systems used for remote data acquisition based on internet will be in high demand in current scenario. Any of them can be used for development of the applications but with the in-built Ethernet controller feature of Cortex M3 processor will surely draw wide attention in developments. The Stellaris family of microcontrollers-the ARM Cortex M3 offers efficient performance and extensive integration, favorably positioning the device into cost-conscious applications requiring significant control-processing and connectivity capabilities.

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International Journal of Electronics Communication and Computer Engineering Volume 5, Issue 1, ISSN (Online): 2249_–071X, ISSN (Print): 2278_–4209

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Dr. Raj Kumar Tiwari

received M.Sc. Degree in Physics with specialization Electronics and PhD degree in Physics. He has been working as faculty in various capacity & currently Head of Department, Physics & Electronics, Dr RML Avadh University, Faizabad. He has 26 years of rich experience of teaching at UG & PG courses. He has produced 9 PhD students. He has more than 53 research publications in various referred journals. He has received various fellowship awards as NET, CSIR (JRF, SRF), Ward Vedant Gold Medal Allahabad University. He is a member of Vigyan Parishad, Prayag and founder member of IAPS Allahabad.

E-mail: rktiwari2323@yahoo.co.in.

Santosh Kumar Agrahari