Based on MSP430 MCU's CAN Bus Interface Card Design

Abstract: IT company's MSP430 MCU is a low-power mixed-signal controller, has a wealth of on-chip peripherals, there is a very broad range of applications. Description based on MSP430 MCU's RS232/RS485 CAN bus communication interface design and implementation of change, focusing on the hardware configuration and software features, electrical theory and software are given.

1 Introduction

Controller Area Network (Controller Area Network, referred to as CAN) is a 20th century German Mercedes-Benz cars 80 to address a number of control equipment and instrumentation data exchange between the development of a serial communication protocol. As a widely used fieldbus various industrial site, according to different needs or master-slave mode, or multi-master manner. CAN bus using the communications media for the twisted-pair cable or other transmission rates up to lMb / s. CAN bus communication network with other differences between two: First, send a message destination address is not included, it focuses on full network broadcasting, based on the station under the message reflected in the nature of the data packet identifier filter, the accept received, should not be collected discarded. The advantage of online access the net, plug and play and multi-station receiver; 2 is particularly enhanced data security concerns, to meet the control system and other high data requirements of the system requirements. In view of its high reliability, unique design, high-speed and long distance, etc., particularly in the industrial field monitoring equipment for the interconnection.

2 Introduction

CAN bus is a bus-type network topology, as shown in Figure l. CAN bus using the unique multi-master transmission mode, each extension data according to need only take the initiative to send, no need to keep polling the host, thereby saving network traffic and improve transmission efficiency.

Based on MSP430 MCU's CAN Bus Interface Card Design

Most of the existing monitoring equipment is used in a 232 or RS 1 RS 485 serial communication, the basis for the formation of the CAN communication network, the author designed a portable CAN bus interface card, the converter card can be used as a lithium battery power supply, low power consumption, small size, light weight, portable to meet the needs.

3 system hardware architecture

Texas Instruments MSP430 MCU is an ultra-low power microcontrollers, voltage range of 1.8V ~ 3.6V. The 16-bit RISC processor through the system, 16-bit CPU, registers, and constant generators integrated to obtain the maximum code efficiency. MSP430 family of ultra-low power microcontrollers are used in industrial control, digital motor control, hand-held devices such as the ideal instrument microcontroller. MSP430F449 MCU used in this design, it has a wealth of on-chip modules: up to 8 12-bit A / D converter, 48 I / O ports, two UART watchdog, two built-in 16-bit timer, available online Simulation of Flash memory, 7 Road PWM output, LCD drivers and so on.

CAN Bus Interface Card portable electrical block diagram of the structure shown in Figure 2, which consists of power supply modules, CAN communication interface circuit, serial level converter circuit, the cache and the LCD module.

Based on MSP430 MCU's CAN Bus Interface Card Design

3.1 CAN Communication Interface Circuit

System hardware to Philips companies SJA1000 CAN bus controller core type, it is a stand-alone CAN bus controller, mainly for industrial environments. It is also Philips Semiconductors PCA82C200 type CAN controller (Basic CAN) in the alternative, through a simple bus connection to be completed SJA1000 CAN bus physical layer and data link layer of all the features. SJA1000 CAN core module from the sending buffer, interface FIFO, acceptance filters and interface management logic component. CAN CAN core module is mainly responsible for the information frame transceiver and CAN protocol implementation, the interface management logic for the main controller SJA1000 interface. During data transmission, the host controller to send the identifier and data into the buffer after the request is sent to start the CAN core module to read the data send buffer, and then packaged into a complete CAN protocol CAN message frame, by transceiver to the bus, send buffer capacity is 13 bytes. Acceptance filter unit for processing the received information is sent to receiver FIFO, the receiver FIFO is 64 bytes. PCA82C250 based CAN bus transceiver is between CAN controller and the physical bus interface, which provides the differential CAN bus controller to send and receive capability. The transceiver relying on pin 8 (RS) can choose the different connections the work of 3 different ways: high-speed, slope control and standby mode. RS pin to ground through the resistor can be connected to the slope of the bus control, the slope is proportional to the current output pin RS. Demands for higher transmission rate applications, typically pin 8 directly to ground to select the high-speed mode. In this mode, the transmitter output transistors simply to open and close as fast as possible, do not take any measures to limit the up and down the slope, it must use shielded cable to avoid RF interference. CAN controller to send and receive ports of the circuit through an optical isolation and PCA82C250 connection, effectively suppress interference into the bus.

3.2 serial level converter module

In this design, MSP430F449 only one USART interfaces, while the CAN converter card with integrated RS232, RS485 2 communication modules, DIP switch selection by the design of interface types. RS232 and RS485 serial port level translator modules were selected to Maxim's MAX3221 and MAX3485.

3.3 Power Supply Module

The entire system in addition to lithium battery power supply, can also use a small external power supply transformers, etc., to meet the needs of different occasions. MSP430F449 use TPS7333 regulator power output as a 3.3V system supply voltage. To ensure the normal data transmission, power circuit also has bq24012 battery charge management circuit to battery low, normal data transmission may affect the timely warning, to remind the replacement battery or charger.

3.4 Caching and LCD module

PC's working time in order to save, She Ji Yong TMS44400 Xing dynamic memory when the expansion of dynamic storage interval, when data is transferred first to read Baotouxinxi Yi Jue Ding is Shi Shi transmission or Huancun operation. MSP430F449 with LCD driver module, the design of the East was the company's EDS805 use liquid crystal display module, with its state of the system features real-time display, data transfer speed, remaining time, it can supply under-voltage alarm.

4 Software Design

MSP430 core structure with high transparency format using reduced instruction (RSIC) design. CAN receive and transmit information, as is done automatically by the CAN controller, the program only from the corresponding buffer to read the corresponding data, and then make the appropriate treatment can be. In this system, the MCU after the completion of initialization tasks into low-power sleep mode, any wake-up interrupt can be in favor of the implementation of the corresponding interrupt service routine. System 2 PC serial port interrupt sources were sent and slave CAN message reception, the benefits of doing so is to avoid as much as possible due to data overrun data caused heavy hair. Figure 3 shows the system CAN initialization process, Figure 4 shows the interrupt service routine processes. Due to space relations, the paper spent receiving an interrupt service routine process, the process generally and to send the opposite process.

Based on MSP430 MCU's CAN Bus Interface Card Design

Based on MSP430 MCU's CAN Bus Interface Card Design

5 Conclusion

This article describes the CAN bus communication interface converter card software and hardware design, expect to study the design of CAN bus applications and help provide some references. The introduction of CAN bus communication interface converter card, a simple structure and strong interference capability, is ideal for distributed measurement and control networks of small and medium composition. With the support of the growing device CAN protocol, CAN device prices will drop further in the automation application will be more extensive.