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Based on the IEEE1451 standard design of a wireless transmitter module

In Electronic Infomation Category: B | on April 18,2011

Abstract: IEEE1451 smart sensor protocol can solve different interoperability and SI4848DY-T1-E3 datasheet and interchangeability among other issues. This selected ZigBee as the underlying communication protocol designed on this basis, a wireless transducer interface module (Wireless Transducer Interface Module, WTIM), and SI4848DY-T1-E3 price and through the module IEEE1451-based data transfer and SI4848DY-T1-E3 suppliers and information exchange.

Introduction

With computer technology and communication technology, standards-based distributed a variety of field measurement and control systems are widely used. The system uses a variety of control bus, such as CAN, LONWORKS, FROFIBUS, HATR, FF and so on. These different bus standard has its own protocol format is not compatible with each other, the expansion of the system bring a lot of inconvenience.

View of this, the International Association of Electrical and Electronic Engineers (IEEE) and the National Institute of Standards and Technology (NIST) jointly launched the IEEE1451 standard to address a variety of different standard bus interface compatibility issues, improve the interaction in various products from different manufacturers exchange and interoperability.

1 IEEE1451 protocol

IEEE and NIST launched the IEEE1451 standard, by defining a set of common communication interface to solve the compatibility problems between different network and ultimately the exchange of the various manufacturers of products and interoperability. The relationship between architecture and protocol stack shown in Figure 1. According to IEEE1451 standard, intelligent sensor network is divided into two modules.


Figure 1 IEEE1451 protocol

overall framework

(1) NCAP (network application processor) module The main executive

network communication module, TIM communications, data conversion. IEEE1451.1 standard definition of its physical model. NCAP is the standard transmitter bus and the bus interface between the private network. This part of the microprocessor integrated in the sensor network from the "brain" role. NCAP also support hot plug.

(2) TIM (Smart Transmitter) module NCAP

connection between the basis and approach can have many different functions TIM. TIM can support a single or several different channels, both connected with the sensor can also be connected with the implementation.

IEEE1451.0: This layer standards include common functions, communications protocols and electronic data forms (TEDS FORMATS). IEEE1451.0 by defining the basic command set and communication protocol interfaces for different physical layer to provide a common, simple standard, so as to enhance interoperability between these standards.

IEEE1451.1: technology for existing networks, the definition of smart transmitter to the network from the standard connection method, the use of object-oriented thinking is the intelligent network defines a standard transmitter the object model and the model of a class definition for each of the software interface.

IEEE1451.2: defines the connection between the sensor and microprocessor digital interface TII. The definition of electronic data forms and data formats, also defines a series of read and write commands, including reading and writing spreadsheets, read sensor data and set the actuator data.

IEEE1451.3: distributed multi-point systems, including digital communication and TEDS formats defined, mainly distributed intelligent sensor systems for point-synchronous data acquisition and communication.

IEEE1451.4: contain mixed-mode communication protocol defines the format and TEDS. The main for existing analog transmitter communication protocol, while support for digital interface to read and write TEDS data, on the other hand support the analog interface on the site of measurement instruments.

IEEE1451.5: definition of wireless smart sensor interface, a wireless communication protocol by specifying the wireless transducer interface module (WTIM) and NCAP to communicate. Currently, WiFi, Bluetooth, ZigBee protocol. IEEE1451.5 also defines communication protocols associated with wireless TEDS.

2 wireless communication protocol

IEEE1451.5 standard for the use of different communication protocols for wireless sensor provides a unified interface, not developing a new wireless communications technology, instead of using wireless communication technology has matured as an interface standard. IEEE 1451.1 standard proposes the three kinds of wireless communication: WiFi, Bluetooth and ZigBee. This paper uses a ZigBee protocol, which mainly include the IEEE 802.15.4 PHY layer and MAC layer, and the NWK layer and the ZigBee APS layer.

2.1 IEEE 802.15.4 PHY layer of

PHY layer uses DSSS technology to provide a different track, different carrier transfer rate, 2.4 GHz to provide 250 kbps transfer rate. PHY layer between the two devices used to provide transparent bit stream. Its main features include: channel selection and channel energy detection, clear channel assessment *, radio channel data transceiver, receive packet link quality.

2.2 IEEE 802.15.4 MAC layer of

MAC layer is responsible for the NWK layer data packets sent to the package, sent to the PHY layer to the next, and the PHY layer to send up the frame decomposition, the decomposition of the data packets sent up to the NWK layer.

MAC layer provides a beacon and non-beacon two transmission modes. Among them, the beacon transmission mode through the network coordinator for a certain time interval broadcast beacon frames to the network, all nodes within the network to the beacon frame as a synchronization signal, the entire network synchronization. Non-beacon transmission mode using CSMA / CA mechanism to avoid the collision.

MAC layer of the main functions of data processing for the MPDU. The frame format including the header, MAC payload and frame the end of three parts. The frame control header field provides a frame type, security is enabled, the destination address mode, the source address mode and other related control information. MAC MAC layer payload field is valid data, that NWK packets. The end of the header and the MAC frame payload field of 16-bit frame check sequence CRC.

2.3 ZigBee protocol NWK layer


Figure 2 NWK frame format

ZigBee Alliance standard in the IEEE 802.15.4 PHY layer developed on the basis of the NWK layer protocol. Its main functions include: network layer protocol data unit processing, network management and routing group. NWK frame format shown in Figure 2.

2.4 ZigBee APS layer protocol

Application layer includes application support layer (APS), application framework (AF) and the ZigBee device object.

Support layer (APS): APS layer includes protocol data unit APDU processing, APS and node data transfer mechanism between the application object binding.

Application Framework (AF): for each user-defined application object provides a template type of activity space for each application object provides a key to the service and message service used for data transmission.

ZigBee Device Object: including equipment service discovery.

3 System Design This module is designed WTIM

. The module is used for collecting and processing data, and through SPZB260 module will send data to the NCAP, while achieving a TEDS (Transducer Electronic Data Sheet), IEEE1451.5 standard. SPZB260 developed specifically for embedded low-power ZigBee modules.

3.1 WTIM module

WTIM modules include STM32F103C microcontroller, SPZB260 modules, signal conditioners and sensors. The structure shown in Figure 3. Which, SPZB260 module to communicate with the NCAP module.


Figure 3 WTIM module chart

ADC samples in the data, using the first-order filtering algorithm: Y (n) = X (n) (1-) + Y (n-1). Where: is the filter coefficient; X (n)-oriented sub-samples; Y (n-1) for the last filter output value; Y (n)-oriented sub-filter output value.

3.2 TEDS

IEEE1451 each layer has a corresponding TEDS. This implements the PHYTEDS, MetaTEDS and TransducerChannel TEDS. The general format is:

StructXXX_TEDS {

UInt32 TEDSlength;

TLV;

... ...

TLV;

UInt16 Checksum;

}

TEDSlength: XXX_TEDS TEDSlength structure in addition to the length of all fields outside.

TLV: a containing type (Type), length (Length), value (Value) structure of three fields.

Type: XXX_TEDS each TLVs ID. For different TEDS, even if the same ID TLVs represent the actual meaning is different.

Length: TLV structure that the length of the Value field.

Value: This field is filled with specific TEDS information.

Checkum: provides XXX_TEDS before the middle of the field (including TEDSlength and all TLV field) checksum.

Checksum is calculated as follows: Checksum = 0xFFFF-TEDSlength +2 i = 1TEDSOctet (i)

3.3 IEEE1451.5 standard implementation

IEEE1451 supports 3 type of wireless communication protocol is implemented in this article ZigBee protocol. IEEE1451.5 ZigBee protocol defines the standard in the module functions, interface functions, as well as between the NCAP and WTIM wireless communication protocol. The protocol stack is defined as shown in Figure 4.


Figure 4 IEEE1451.5 standard protocol stack

PHY layer, MAC layer, NWK layer provided by the SPZB260. This article need to implement APS layer and IEEE1451.5 convergence layer.

APS layer protocol is used in EZSP, through SPI interface. In WTIM module, STM32F103C and SPZB260 through SPI communication between them STM32F103C configured as SPI master device, SPZB260 configured as a slave. EZSP as IEEE1451 5 convergence layer of the application support layer (APS), the NCAP star for the coordinator to achieve the network structure shown in Figure 5.


Figure 5 IEEE1451.5 the network topology

IEEE1451 5 convergence layer defines the IEEE1451 5 and IEEE1451 0 communication interface between the modules. Among them, the part of the interface provided by the IEEE1451.5 system was IEEE1451.0 called; another part of the IEEE1451.0 available.

4 tests and conclusions

In the test, for the temperature sensors and humidity sensors. Test WTIM two nodes, each node has a temperature sensor and humidity sensor. Which, WTIM1 on normal circumstances, the other node WTIM2 placed in the top of a container filled with water. Through the ZigBee NCAP to communicate with two nodes and can be monitored by the host. Measurements at 10 Hz sampling frequency, the results shown in Figure 6.


Figure 6 WTIM1 the temperature and humidity data

Test results show that, WTIM node to resume normal access to the data sent to NCAP, making access to the NCAP to the correct channel information node and the response, to achieve a wireless transmitter function.

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