Design of wireless communication module based on CC1020

Introduction

With the rapid development of network and communication technology, wireless communication has broad application prospects in many fields due to its low cost, good scalability, few restrictions on geographical conditions, simple and flexible installation and construction.

Introduction to CC1020

CC1020 is an ideal ultra-high frequency monolithic transceiver chip. It is mainly used in the ISM (Industrial, Scientific Research and Medical) frequency band and SRD (Short Range Device) in the 426/429/433/868/915MHz frequency band. It can also be used after programming for frequencies of 402MHz~470MHz and 804MHz~940MHz multi-channel equipment.

The main operating parameters of CC1020 can be programmed through the serial bus interface, such as output power, frequency and AFC.

In receive mode, the CC1020 can be regarded as a traditional superheterodyne receiver. After the RF input signal is amplified by the low-noise amplifier (LNA and LNA2), it is flipped through the integrator (I and Q) to generate an intermediate frequency IF signal. In the IF processing stage, the I/Q signal is mixed, filtered, amplified and converted into a digital signal by the ADC. Then perform automatic acquisition control, channel filtering, demodulation and binary synchronization processing, output digital demodulation data on the DIO pin, and obtain synchronous digital clock data on the DCLK pin. RSSI is in digital form and can be read out via the channel interface. RSSI also serves as a programmable carrier sense indicator.

In transmit mode, the resultant RF signal is fed directly to the power amplifier PA. The RF output is the FSK signal, which is generated by FSK modulation of the digital bit stream fed to the DIO pin. A high frequency filter can be used to obtain Gaussian frequency shift keying GFSK. The receive/transmit switch circuit inside the chip makes the antenna easy to access and match.

Hardware circuit design

Microcontroller selection

Microcontroller uses C8051F310 produced by Cygnal Company. This processor has a CIP-51 core that is fully compatible with 8051. It is a fully integrated mixed-signal ISP type MCU chip with analog multi-channel The device's 10-bit 200ksps 25-channel single-ended/differential ADC, hardware-implemented I2C, enhanced UART and SPI interfaces, Flash memory with in-system reprogramming capability, can be used for non-volatile data storage, and allows field updates of 8051 firmware . This type of microcontroller is small in size, has high performance, can quickly access data, and is easy to develop and expand the system. It is very suitable for the needs of this design.

CC1020 structure configuration interface

The connection between the CC1020 structure configuration interface and the microcontroller is shown in Figure 1. The microcontroller uses pins P2.2~P2.5 to connect to the structural configuration interfaces PSEL, PCLK, PDI, and PDO of CC1020. The PDO is connected to an input of the microcontroller. PDI, PCLK and PSEL are connected to the outputs of the microcontroller. If PDI and PDO are connected together, the microcontroller can use a bidirectional pin terminal, which saves an I/O port of the microcontroller.

When the fabric configuration interface is not in use, the microcontroller pins connected to the PSEL, PCLK, PDI and PDO pins can be used for other purposes. When the PSEL pin is inactive (maintained high) (the PSEL pin is active low), PCLK, PDI and PDO are in a high-impedance input state. PSEL has an internal pull-up resistor that must be disconnected (tri-stated by the microcontroller) when in low-power mode, or set high to prevent current from flowing into the pull-up resistor.

The CC1020 is programmed via a simple quad serial SPI interface. There is an 8-bit structure configuration register. The address of each register is 7 bits, and 1 bit is used as a read/write bit to initialize the read or write operation. A complete configuration of CC1020 requires sending 33 data frames, each frame has 16 bits (Address 7 bits, R/W 1 bit, Data 8 bits). The time required for a complete configuration depends on the PCLK frequency. If the PCLK frequency is 10MHz, the time to complete a complete configuration is less than 53ms. Setting the CC1020 into low power mode only requires one frame of data to be sent, so the time required is less than 2ms. All registers are readable.

CC1020 signal transceiver interface

The connection between the CC1020 signal transceiver interface and the microcontroller is shown in Figure 1. The microcontroller uses pins P2.6 and P3.4 to connect to the bidirectional synchronous data interface DIO and DCLK of the CC1020.

Figure 1 Connection circuit between CC1020 and microcontroller

A bidirectional pin of the microcontroller is connected to the DIO of the CC1020 for data transmission and reception (input and output). DCLK provides data timing and must be connected to an input of the microcontroller.

Data output can optionally use a separate pin. At this time, the INTERFACE register SEP_DI_DO=1 of CC1020 must be set. In synchronous mode, the LOCK pin is used as data output, the DCLK pin is used as data output in asynchronous mode, and the DIO pin is only used for data input.

One pin of the microcontroller can be used to monitor the lock signal of the phase-locked loop, that is, the LOCK pin signal. When the phase locked loop is locked, the LOCK pin is logic low. It can also be used for carrier detection and monitoring of other internal test signals.

CC1020 can be set to three different data transmission modes: synchronous NRZ mode, synchronous Manchester code mode and asynchronous transmission UART mode. Each of these three modes has its own characteristics. Synchronous Manchester code has the best anti-interference ability, but the baud rate is twice as low. Asynchronous transmission UART is the easiest to implement, but has the worst anti-interference ability. Synchronous NRZ has better anti-interference ability than UART. , but slightly worse than the synchronous Manchester code, and the implementation difficulty is also between the two. Considering that microprocessors basically support UART serial communication, this mode was chosen, and the tested results can fully meet the requirements.

CC1020 Antenna Selection

CC1020 can use various types of antennas. Antennas commonly used in short-range communications are monopole antennas, helical antennas and loop antennas. This design uses the best range and simple 1/4 wavelength monopole antenna.

Power Management

CC1020 provides very flexible power management to adapt to the strict power consumption requirements in battery-driven applications. Low power mode is controlled through the MAIN register and POWERDOWN register. There are independent bits in the MAIN register for controlling the receiving section, transmitting section, frequency synthesizer and crystal oscillator. This independent control method allows the power consumption of each application to be optimized to a minimum. Since this design is a separate wireless communication module, the power consumption requirements are not too strict. The system uses 5V power supply and stably outputs 3V voltage through NCP500.

Anti-interference measures

The radio frequency transceiver system is very sensitive to power supply noise, so the design adopts the method of separately powering the radio frequency part and other circuits. High-frequency devices are sensitive to noise, so filters or voltage regulators are installed on each part of the power supply to reduce the interference of power supply noise on the chip. In addition, power monitoring and watchdog circuits are used on the chip to greatly improve the anti-interference performance of the entire circuit.

Chipcon provides a circuit reference design for the radio frequency part. The layout of the radio frequency part refers to the layout of the reference design, and some changes are made according to the actual situation to obtain the best effect. CC1020 has very few peripheral components, among which the VCO inductor is a key component. A high-precision inductor is selected, and the layout is as close to the chip as possible, and the two input pins are made as symmetrical as possible to ensure performance. In addition, during the design, the crystal oscillator and the chip pins were kept as close as possible, and the clock area was isolated with a ground wire. The crystal oscillator shell was grounded and fixed, and a metal cover was used to electromagnetic shield the radio frequency part. The above measures are used to ensure the reliable operation of the system.　

Figure 2 Main program flow chart
　
software design

communication protocol uses UART format (one start bit, load data, one end bit). In addition, there is a synchronization code before the data packet. The function of the synchronization code is to enable the receiving chip to correctly identify the UART format data. . There must be an identification code afterwards. The identification code is used to mark the start of the data. If the identification code is received correctly, it means that the data can be received correctly. If the data length is not certain, add a length code to the beginning of the data packet, or add a specific end flag to the end of the data packet. In order to cope with possible data errors during wireless transmission, a check code is added at the end of the data packet, so that the packet can be discarded or retransmitted according to application needs. In practical applications, it is found that after the data packet, it is best to have 1 to 2 bytes of redundant code. Otherwise, the last byte of data is easily interfered by noise, causing misidentification. The main flow chart is shown in Figure 2.
　　　　
Conclusion

This communication module has the characteristics of low cost, strong versatility, strong scalability, and high reliability. It can be used alone or can be easily integrated into various wireless measurement and control systems as a system expansion module. References: 1. Lu Yan, Li Jun, Bao Hong. Design of wireless communication system based on NRF401. Mechanical and Electronics. 2004.09 2. Wu Qiuming. Development of miniature low-power RF transmitter. Measurement and Control Technology. 2004.1 VOL23 3. Chipcon . The Data Sheet of CC1020.http://www.chipcon.com