Specific Application of Single Chip Microcomputer in Industrial Wireless Network

Just as many general-purpose microcontrollers (MCUs) today have integrated USB, CAN and Ethernet as standard peripherals inside the chip, more and more wireless network chips and wireless network solutions are also developing towards integrated SoC, such as the first-generation products, Nordic's nRF905, Chipcon's cc1010, which integrate 8051-compatible microcontrollers. These wireless microcontrollers are suitable for general point-to-point and point-to-multipoint private network applications, such as single-product remote controls and meter reading devices. Wireless communication technology provides a convenient way for the interconnection and intercommunication of intelligent devices. As a network technology for industrial and home automation, industrial wireless networks are also developing towards intelligence, standards and energy saving.

Typical Industrial Wireless Networks

Currently, wireless network technologies used in industrial control and consumer electronics include ZigBee, wireless LAN (Wi-Fi), Bluetooth, GPRS general packet radio service, ISM, IrDA, etc. In the future, there will be 3G, ultra-wideband (UWB), wireless USB, Wimax, etc. Of course, there are also a large number of private and dedicated wireless networks used in industrial control and consumer electronic devices, among which ZigBee and GPRS are the two most discussed and used in domestic industrial control. Bluetooth and wireless LAN are wireless protocols widely used in consumer electronic products such as mobile phones, headphones, printers, cameras and home small and medium-sized enterprise networks (some industrial products also have applications, such as wireless video surveillance and car audio systems). Of course, private wireless network technologies and products also have many applications in industry.

ZigBee is a low-power, short-distance and low-speed wireless network technology that operates at the 2.4GHz international license-free frequency. In the IEEE standard, it belongs to the wireless personal area network in the 802 family together with wireless LAN and Bluetooth. ZigBee consists of two parts. The physical and link layers comply with IEEE802.15.4, and the network and application layers comply with the specifications of the ZigBee Alliance. The ZigBee Alliance (www.zigbee.org) is a non-profit organization established in 2002. It has more than 200 members including TI, Honeywell, and Huawei. The ZigBee Alliance is committed to promoting platforms compatible with 802.15.4 and ZigBee protocols, formulating public specifications for the network layer and application architecture, and hopes to popularize the ZigBee standard in building automation, home control, home appliances, industrial automatic control, and computer peripherals.

GPRS is a packet data bearer service developed from the existing GSM network. It works on the standard GSM frequency. As a packet switching system, it is suitable for sudden and small amounts of data transmission in industry. Also, because the GSM network has a wide coverage and is always online, GPRS is suitable for remote monitoring and measurement systems in industrial control. In industrial control applications, GPRS chips generally appear in the form of wireless data transmission modules, which are connected to the microcontroller through the RS232 full-duplex interface. In terms of software, these modules have built-in GPRS, PPP and TCP/IP protocols. The microcontroller side sends test, connection and data transmission and reception instructions to the module through the AT instruction set. The GPRS module enters the Internet and communicates with other terminals or servers through China Mobile's cmnet. At present, the common modules on the market include Siemens G24TC45, TC35i, Freescale G24, Sony Ericsson GR47/48, and Wavecom's GPRS SoC module WMP50/100 with integrated ARM9 core. GPRS modules are divided into two types: those with built-in TCP/IP protocol and those without protocol. Generally speaking, if the microcontroller side has an embedded operating system and TCP/IP protocol support or the application requires only sending and receiving text messages and voice functions, you can choose a module without protocol.

Wireless MCU

Advanced SoC technology is playing an important role in the field of wireless applications. The CC2430 released by Texas Instruments after acquiring Chipcon is the first SoC ZigBee microcontroller on the market, as shown in Figure 1. It integrates the protocol stack z-stack in the flash memory inside the chip, has a stable and reliable CC2420 transceiver, an enhanced 8051 core, 8KRAM, and peripherals I/O ports, ADC, SPI, UART and AES128 security coprocessor. The three versions are 32/64/128K flash memory. Taking 128K as an example, after deducting the basic z-stack protocol, there is still 3/4 of the space left for application code. Even if the complete ZigBee protocol is included, there is still nearly 1/2 of the space left for application code. In addition to processing communication protocols, such wireless microcontrollers can also complete some monitoring and display tasks. Such wireless microcontrollers support integration with general microcontrollers or embedded CPUs through SPI or UART. The CC2480, a new generation single-chip ZibBee certified processor released in April 2008, demonstrated an example of combining it with TI MSP430 general-purpose low-power microcontroller.

Figure 1 CC2430 application circuit

Another chip giant in the field of industrial control, Freescale's single-chip ZigBee processor MC1321X, has a very similar solution, integrating the HC08 microcontroller core, 16/32/64K flash memory, GPIO, I2C and ADC peripherals, and Beestack software. However, the maximum 4K RAM is a bit small for more tasks. However, with the experience and advantages of 32-bit microcontroller Coldfire and system software, Freescale has made more distinctive efforts in meeting the flexible needs of user applications. It is the first to provide solutions from low-medium-high levels, as shown in Figure 2.

Figure 2 Freescale ZigBee solution

GPRS SoC wireless microcontrollers represented by Wavecom are also performing the revolution of GPRS wireless processors. For example, WMP50 is an industrial processor with quad-band GSM network wireless communication, built-in ARM9 CPU, supporting 128K flash memory, 128K RAM, 11 GPIO, I2C, SPI, 5X5 keyboard, 2 UARTs, USB 2.0 parallel port, ADC, DAC, etc. WMP50 has a mandatory real-time multi-tasking operating system, which supports application tasks to work at a higher priority than GPRS tasks, that is, it can ensure control response requirements. In short, both GPRS wireless microcontrollers and ZigBee microcontrollers are moving towards lower costs, more standardization and higher performance. In April 2007, the up-and-coming Jennic launched a $5 Zigbee/IEEE802.15.4 reference design. This price includes the BOM cost of the JN5139 32-bit wireless microcontroller PCB antenna design and other auxiliary components. It is said that the RF performance can reach a distance of 1 km.

Wireless System-on-Chip

Wireless microcontrollers with C language development and debugging tools can be competent for the system design of a transmission or receiving module. For example, a wireless sensor node designed using CC2430, IAR embedded workbench (EW) compilation and debugging tools and TI z-stack simpleAPI, users can use TinyOS or uc/OS-II for wireless sensor networks, or do not use embedded operating systems. For another example, for wireless remote meter reading terminals, you can use MSP430 or CYGNAL C8051 or HC08 microcontrollers and a wireless data transmission module, such as G24. The development tools can use KEIL IDE or IAR EW430/8051, or codewarror. G24 has built-in TCP/IP and GPRS protocols. Through the use of AT command testing, access to the Internet, connection to the server, and the operation of sending and receiving data, the GPRS wireless communication task is completed. The microcontroller completes the meter data collection task through sensors. However, if you plan to design a smart home communication node, such a wireless microcontroller will not be able to meet the needs, because in addition to collecting indoor environment (such as temperature, humidity), electricity, water and gas meter data, household appliance switches and home security alarms through the ZigBee network, another very important function is that this node should also be connected to the home server through a wired Ethernet network or a wireless Wi-Fi network. This server is the core of the home PC, TV, video, and audio. The smart home communication node, home server and Internet (community broadband) router form a home network system.

To design and implement such a communication node requires certain system software support and a certain amount of processor power. Because it is an industrial device, its reliability, security, power consumption and ease of operation are much more stringent than those of household appliances. There are two design methods currently seen. One is to use a large-scale embedded operating system, such as Linux and WinCE, which have good network and device driver support capabilities. The cost is that an ARM9 or higher MMU embedded processor, more than 32M storage space and more than 32M execution space (WinCE requirements may be even higher), such as the industry-leading wireless sensor network platform company Crossbow's imote2 (aggregation node) uses a Marvell 416 MHz PXA271 processor and a TI ZigBee transceiver. The benefits of such a design are obvious, but the problem that may arise is how to control the power consumption and reliability of the system. Most industrial wireless networks are installed in an unmanned site, or in a harsh natural environment. Whether it is open source Linux, commercial embedded Linux, or WinCE power management technology is not yet perfect, and the system boot and recovery functions and time cannot fully meet the requirements of industrial control applications. Another alternative is the solution currently recommended by many MCU semiconductor companies; the hardware is ST, NXP ARM microcontrollers and Freescale coldfire microcontrollers, such as MCF52335, and the system software is Nichelite coldfire TCP/IP Lite, a free and lightweight embedded TCP/IP software for coldfire, which is a collaboration between Interniche and Freescale. It includes TCP, UDP, ICMP, DHCP (client), TFTP and a simple non-preemptive RTOS (www.freertos.com), with only about 20K of code, plus Freescale's Web server and Flash file system, which can meet the application of industrial network convergence points. Of course, if these free software modules still cannot meet the application requirements, Interniche also has PPP, SNMP, DHCP (server), FTP server, IPSEC, RTP and other module options, and even upgrades to the full-featured version of nichestack. ST ARM and NXP LPC microcontrollers also have similar solutions based on Nichelite. The advantage of this solution is that the MCU can use a low-frequency ARM/coldfire Flash microcontroller, which reduces power consumption and increases reliability. The system software is licensed to users free of charge by semiconductor companies, so users only need to purchase conventional microcontroller development tools such as IAR EW, ARM MDK, and Codewarrior to complete the design task of an industrial network communication node. The development difficulty and overall product accounting cost are low.

Looking further, traditional single-chip microcomputers are making great strides into all aspects of the industrial wireless network field. In addition to the previous SoC single-chip wireless microcontrollers, such as TI's recent SimplicTI, a TI private RF network, can also be said to be a simplified ZigBee network solution. Compared with the ZigBee protocol, SimplicTI supports point-to-point and star networks, with only 4K code, and is very simple in structure and use. A TI MSP430 16-bit microcontroller plus RFCC1100/CC2500 can form a smoke sensor, gas leak alarm and meter reading node design. The development of SimplicTI is still a typical single-chip system. Using the IAR EW430 tool, the RF protocol software and library programs are all provided by TI for free with source code. The API of SimplicTI has only 6 functions: initialization, connection and monitoring, sending and receiving, configuration, and the configuration parameters are simple and clear, including frequency, security token, network topology (point-to-point, star), power management and memory allocation. IAR of Sweden has recently transplanted Powerpack RTOS and supported the development of MSP430 MCU, which makes the design of 430 wireless nodes more complex and flexible under the support of RTOS. Figure 3 is SimplicTI development board, chipcon radio interface, you can install CC1100/2500 devices. According to TI data, SimplicTI will also support the upgrade of ZigBee wireless MCU such as CC2430 in the future. CC2430 support SimplicTI also means that TI's support for wireless networks is more extensive and flexible, and upgrading is convenient.

Figure 3 SimplicTI development board

Conclusion

Wireless technology is one of the fastest-growing areas of embedded systems in the future. MCU is the most traditional core component of embedded and industrial control systems. The development of SoC and microelectronics manufacturing processes has promoted the transformation of MCU. Wireless technology and application is a hot spot in the development of MCU, and it is an important stage for industrial chip semiconductor giants including TI, Freescale, ST, NXP, Atmel, Microchip and professional wireless companies Ember, Jennic, Nordic. Whether it is SoC wireless MCU that integrates RF devices and MCU core, or wireless SoC with MCU plus RF devices or RF MCU, they will be embedded in various electronic devices in the future. Due to the particularity of the industry, the wireless network of industrial control system has many factors that determine the selection of a wireless network technology, such as communication range, environmental interference, connection method, rate and power consumption, but it will gradually move from private mode to general direction. Just as we see today that Ethernet and CAN bus are the mainstream networks of the new generation of industrial design, the use of standard wireless networks in industrial control systems, such as ZigBee, GPRS, Wi-Fi, Blutooth, which we can see today, will be more and more applications, and it will be the general trend in the future.

However, it should be pointed out that in certain special environments and conditions, shortwave and satellite communications are still used in industrial wireless networks. For example, the automatic water condition monitoring and reporting system after the Wenchuan earthquake in Sichuan is composed of Beidou satellites, satellite terminals, transmission equipment and solar power supply devices, which enables remote industrial wireless network equipment to operate normally in earthquake-stricken areas where basic communication methods cannot be guaranteed.