Main performance of RF IC (A7105) Operating frequency: 2400~2483MHz ISM band (global license-free application band). Working distance: within 10m; The proprietary solution adopts the channel mode of Bluetooth. The proprietary solution divides the frequency band between 2.400~2.483GHz into 166 channels with a bandwidth of 500KHz, while Bluetooth is divided into 83 channels and ZigBee is 16 channels (see Figure 2). Compared with Bluetooth and ZigBee, this makes the A7105 proprietary solution have more available frequencies when encountering interference from crowded frequency bands. Interference Handling All three wireless technologies, Bluetooth, ZigBee and the proprietary scheme, have mechanisms to reduce interference from RF devices operating in the same frequency band. Bluetooth has a frequency hopping spread spectrum (FHSS) mechanism that ensures that the 79 1MHz channels are evenly covered to avoid constant channel interference. ZigBee uses its 16 frequency bands to deal with narrowband interference, so it is more susceptible to interference when other 802.11b/g devices are present, which may require waiting for the other device to stop transmitting. The proprietary scheme takes a more flexible hybrid approach. Because its output power is moderate, interference is less likely to occur. To minimize current consumption and complexity, the proprietary solution does not use spread spectrum mode and simply transmits at a single frequency until a packet arrives in the event of interference. If the frequency needs to be changed during transmission, a single byte command is simply sent via SPI. With 166 500KHz channels, frequencies can be reallocated to avoid other devices transmitting on the same frequency, and even in "hot spots" such as airports, frequencies are not often reallocated for minutes or even hours. Comparison of the proprietary solution with the other two solutions First, the disadvantages of using Bluetooth and ZigBee solutions: First, in order to comply with the standard, you have to meet the standard, which will cost you a high NRE fee to start designing and testing compatibility. Second, due to its nature, standards must be a "one size fits all" solution - in an increasingly competitive global market, your competitors have the same technology as you, making it difficult to distinguish the advantages of your product. Finally, standards provide little design flexibility; for example, efforts to reduce power consumption in your RF products will be limited. Advantages of proprietary solutions: low cost, nRF proprietary solutions do better than Bluetooth and ZigBee in terms of requiring a product to have long battery life and reliable communication and achieve low duty cycle. Explanation of related terms: FSK (Frequency-shift keying) is an early modulation method used in information transmission. Its main advantages are: it is easier to implement and has good noise and attenuation resistance. It has been widely used in medium and low-speed data transmission. The most common is the dual-frequency FSK system that uses two frequencies to carry binary 1 and 0. Technically, FSK has two classifications, incoherent and coherent FSK. In incoherent FSK, the instantaneous frequency shifts between two discrete values named mark and space frequency, respectively. On the other hand, in coherent frequency shift keying or binary FSK, there is no discontinuity in the output signal. Gaussian frequency shift keying GFSK - Gauss frequency Shift Keying, is to limit the spectrum width of the signal through a Gaussian low-pass filter before modulation. GFSK Gaussian frequency shift keying modulation is a digital modulation method that pre-modulates and filters the input data through a Gaussian low-pass filter before performing FSK modulation. It can control the spectrum of the modulated signal by changing the 3dB bandwidth of the Gaussian low-pass filter while maintaining a constant amplitude. It has the desired characteristics of wireless communication systems such as constant amplitude envelope, concentrated power spectrum, and narrow spectrum. Therefore, GFSK modulation and demodulation technology is widely used in many fields such as mobile communications, aviation and marine communications. Channel distance: 500KHz, total number of channels: ~160, that is, the effective frequency range is 2400~2483MHz, and a channel can be set every 500KHz interval. Different RF devices in the same space can be set to work in different channels through frequency hopping to reduce interference. Low receiving power consumption: 500Kbps@16mA; Low sending power consumption: 0dBm@19mA; Sleep current: <1μA; Output power: 0dBm; Sensitivity: -110dBm@2.5KBPS, -104dBm@25KBPS,-97dBm@250KBPS,-93dBm@500KBPS, Data transmission rate: up to 500Kbps; Basic applications: mouse, keyboard, toys, etc. Data transmission rate: up to 500Kbps; Basic applications: mouse, keyboard, toys, etc. 3: RF system diagram and interface definition with MCU For RF IC-A7015, its control is through SPI (3 or 4 wire) serial interface operation to read or write data (SCS, SCK, DIO or GIOx). If you want to use a 4-wire serial interface, first make sure to use GIO1 or GIO2 pin for SPI data out. Interface pin description for MCU and A7105: SCS: SPI enable; SCK: SPI clock signal; SDIO: SPI data signal; GIO1: Multiplex signal input/output 1, SPI data1; GIO2: Multiplex signal input/output 2: SPI data2; MCU and RF IC communicate via SPI. The format of SPI is shown below 4. Two data transmission modes of RF IC (A7105) RF IC working mode: There are two working modes, one is direct mode,The second is FIFO mode. Different working modes can be set by the corresponding registers during initialization. Direct mode: Provides users with an RF channel. At the Tx end, the system transmits data to the RF DATA IO PIN. RF only modulates the data and then transmits it. The RX end uses digital demodulation to restore the data. FIFO mode: The timing is as follows: 1): Tx data transmission timing: First use SPI to write data into Tx FIFO (up to 64 bytes can be written), write commands, make RF IC enter Rx mode, start transmitting data, and return to the original state after the transmission is completed. 2): Rx data transmission timing: Write command to make RF IC enter Rx state. When the same ID CODE is received, PIN RX_SYN will be set to 1. At this time, the received data begins to be written into Rx FIFO. After completing the reception of a data packet, it automatically leaves Rx and returns to the original state. Five: Implementation method of RF communication between A7105 and MCU 1. How to pair (link) two RF ICs: Before two RF ICs communicate, they must be paired (Link). When transmitting and receiving data, the two RF ICs use the same ID and channel so that they can communicate normally. When pairing, Master and Slave usually use the same frequency. For example, when Master is used as Tx, the frequency is set to 2.405GHz, and when Slave is used as Rx, the frequency is set to 2.4055MHz. That is, Tx should have a bandwidth higher than Rx (500KHz). The steps of Link are as follows: Host (Key/mouse end) On the slave end, only when entering the pairing mode, it enters rx_mode to detect whether the ID code is received. If it is received, the working state is switched to Tx_mode, and the default data is sent to the host, indicating that the pairing is OK, and the received RF ID is saved at the same time. 2. Related processing of RF anti-interference 1): The difference between frequency hopping and spread spectrum The frequency hopping step is 20MHz. Direct spread spectrum: Direct sequence spread spectrum (DS) working mode, referred to as direct spread mode (DS mode). It is to use a high-speed spread spectrum sequence to expand the spectrum of the signal at the transmitting end, and use the same spread spectrum code sequence to despread at the receiving end to restore the expanded spread spectrum signal to the original signal. The direct sequence spread spectrum method directly modulates the carrier with a pseudo-noise sequence. The data information to be transmitted needs to be channel coded, and then modulo-2 and generate a composite code with the pseudo-noise sequence to modulate the carrier. After receiving the transmitted signal, the receiver first captures the precise phase of the transmitted pseudo code through the pseudo code synchronization capture circuit, and then generates a pseudo code phase that is completely consistent with the pseudo code phase of the transmitter as the local despread signal, so that the data information can be restored in time and the signal reception of the entire direct spread communication system can be completed. Frequency hopping: Frequency hopping technology is completely different from direct sequence spread spectrum technology and is another kind of spread spectrum. The carrier frequency of frequency hopping is controlled by a pseudo random code. Within its working bandwidth, its frequency synthesizer continuously changes the frequency according to the random law of the PN code. At the receiving end, the receiver frequency synthesizer is controlled by the pseudo random code and maintains the same change law as the transmitting end. Frequency hopping is a spread spectrum in the sense that the carrier frequency continuously jumps within a certain range, rather than spreading the transmitted information, and will not obtain the processing gain of direct sequence spread spectrum. Frequency hopping is equivalent to an instantaneous narrowband communication system, which is basically equivalent to a conventional communication system. Since it cannot resist multipath and has low transmission efficiency, the frequency hopping system with the same transmission power has a smaller effective transmission distance than the direct spread system. The advantage of frequency hopping is anti-interference, and fixed-frequency interference will only interfere with some frequencies. When it is used for voice information transmission, it will not have a great impact on voice communication when fixed-frequency interference only accounts for a part. The hopping speed directly reflects the performance of the frequency hopping system. The higher the hopping speed, the better the anti-interference performance. The military frequency hopping system can reach tens of thousands of hops per second. In fact, the mobile communication GSM system is also a frequency hopping system, and its specified hopping speed is 217 hops per second. For cost considerations, the hopping speed of commercial frequency hopping systems is very slow, generally below 50 hops/second. Since the slow hopping frequency hopping system can be easily implemented, low-speed wireless LAN products often use this technology. 2): Two methods for RF IC to achieve anti-interference in communication Under normal circumstances, frequency hopping in the strict sense is only used in military and high-end GSM and other wireless communication systems. For low-cost RF communication systems, because their own transmission distance is short (within 10M), the mutual interference is small, so it is possible to let Tx transmit multiple times until Rx receives and returns the receiving flag. The other method uses a limited frequency hopping working mode, that is, after the data is transmitted, it is determined whether Rx has received it. If it has not received it, the transmission frequency is changed (for example, increase 20MHz), and then a synchronization signal is sent to Rx, and then the transmission continues. This method is simple to implement, but the anti-interference performance is worse than the strict frequency hopping method. 3. How MCU communicates through RF IC MCU can be divided into two types according to its memory type: no on-chip ROM type and on-chip ROM type. For chips without on-chip ROM, an external EPROM must be connected to it for use (the typical chip is 8031). Chips with on-chip ROM are further divided into on-chip EPROM type (the typical chip is 87C51), MASK on-chip mask ROM type (the typical chip is 8051), on-chip FLASH type (the typical chip is 89C51), etc. Some companies have also launched on-chip One Time Programming,OTP) chip (typical chip is 97C51). MASKROM MCU is cheap, but the program is fixed at the factory, suitable for applications where the program is fixed; FALSHROM MCU program can be repeatedly erased and written, very flexible, but the price is high, suitable for price-insensitive applications or development purposes; OTPROM MCU price is between the first two, and at the same time has one-time programmable capability, suitable for applications that require both flexibility and low cost, especially electronic products with constantly updated functions and need to be mass-produced quickly. After the two RF chips are aligned, they can be used to transmit data. Rx first demodulates the received signal, and then confirms it with the RF ID code stored in itself. After the judgment is consistent, it starts to store the received data and checks the data according to the corresponding FEC or CRC bits. After the reception is completed, the MCU reads the FIFO of Rx to get the transmitted data. The two data transmission modes are: Direct mode and FIFO mode. 6: Working status and mutual conversion of RF IC (A7105) A7105 RF CHIP has 6 main states, sleep state, STB state, WPLL state, TX state, CAL state. 1. SLEEP state: When entering the sleep state, the internal reference voltage source (band gap) and crystal oscillation circuit of the chip will be turned off. 2. STB state:STB state includes IDLE mode, Standby mode and PLL mode.RF IC enters any mode according to the strobe command. 1) In IDLE mode, the internal reference voltage source of IC is turned on, while the crystal and PLL are turned off 2) Standby mode:When power is on or reset, RF IC will enter standby mode. At this time, the regulator, reference power supply and crystal are turned on 3) PLL mode:The internal reference voltage source, oscillation and PLL of IC are all turned on. 3. WPLL (waiting PLL) state: When any state enters the TX/TX state, it will enter this state or directly bypass the state and enter the Tx/Rx state based on the current state or whether the setting value of the control register PLL I, PLLII, PLL III, PLL IV changes. 4. TX/RX state: The RF IC will decide whether to enter the TX or RX state according to the gating command (strobe command). When using the RFO mode to work in the TX STATE, the RF chip will automatically transmit the TX packet (Preamble+ID+TX FIFO payload). If the transmission is completed, the RF chip will return to the original state. When using the FIFO mode to work in the RX state, the RF chip will enter the RX state waits for Tx data. If the Tx end does have transmitted data, then when the ID code is judged correctly and the set data length is received, the RF chip will automatically return to the original state. 5. CAL state: In the CAL state, there are three independent calibration items. In the STB state, when the corresponding registers are enabled, it will enter the IF filter calibration, VCO band, VCO current calibration procedures. After completing the calibration procedure, the corresponding flag is cleared and returns to the STB state. VII: Matters needing attention in the application of RF IC (A7105) 1. The operating current and operating voltage of A7105, and how to enter the power saving mode When the IC works in the Rx state, the maximum current consumption: 16mA; when working in the Tx state, the maximum current consumption: 19mA; RF output maximum power: 0dbm; After transmitting/receiving data, if the system wants to save power, it can enter the SLEEP mode with a current consumption of <1uA. RF After the IC has completed its work, the MCU can directly send a Strobe command to put it into the SLEEP state. However, it should be noted that before entering the SLEEP state, TWOR or WOR must be set first. 2. Working process of power saving mode (TWOR and WOR introduction) TWOR (Wake up On Radio using Timer): The RF IC has a built-in timer and a low-speed RC OSC. When the system wants to save power, it can put the system into the SLEEP state. After that, at a certain interval, a signal is sent to wake up the MCU to resume the working state and process RF events. This is the TWOR function. WOR (Wake up On Radio): It also uses the built-in timer or low-speed RC OSC of the RF IC. When the time is up, it only wakes up the RF IC to enter the working state, unless a signal is received to wake up the MCU to receive data. 3. Data transmission rate: The minimum transmission rate is: 10KBps, the maximum is 500KBps, but when transmitting data, the closer to the upper limit of the transmission rate, the lower the receiving sensitivity of the Rx end. That is, when the minimum transmission rate is met, appropriately reducing the transmission rate can improve the Rx receiving sensitivity and expand the receiving distance. 4. The operating frequency and number of working channels of RF IC (A7105) The operating frequency of A7105 is 2400~2483MHz, that is, when initializing Tx/Rx, the operating frequency must be set within this range. The bandwidth occupied by each channel is 500KHz,That is, there are about 160 channels in the frequency range of 2400~2483. 5. When setting the operating frequency of Tx and Rx and converting between them during operation, it should always be ensured that the frequency of Rx differs from that of Tx by an intermediate frequency (500KHz for A7105), which is the same as other RF systems. 6. Application scope of A7105 As a low-cost RF transmission/reception solution, A7105 is used in situations where the amount of data transmitted is relatively small, the cost is low, and the standby current is small. Examples include wireless remote control, wireless mouse, wireless keyboard, and wireless joystick.
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