We discussed the two types of Universal Peripheral Interfaces in embedded systems UART and SPI in Chapter Ⅰ. Now let’s learn about I2C, ADC, and CAN bus in Chapter Ⅱ. What Is I2C? I2C (Inter-Integrated Circuit) is a two-wire serial, half duplex bus developed by Philips, mainly used for communication between chips at close range and low speed. It is a widely used bus standard in the field of microelectronic communication control. It is a special form of synchronous communication, with advantages such as fewer interface lines, simple control methods, and small device packaging. I2C can transmit information between multi-master and multi-salve nodes using only two wires: SDA (serial data) and SCL (serial clock). The serial 8-bit bidirectional data transmission rate can reach 100 Kbit/s in standard, 400 Kbit/s in fast mode, and 3.4 Mbit/s in high-speed mode. The device connection is shown in Figure 1. Figure 1 I2C Bus Master to Slave Connections How Does I2C Work? The data on the SDA line must be stable during the high period of the SCL line. The HIGH or LOW state of the SDA line can only change when the clock signal on the SCL line is low. Figure 2 The Synchronous Data Signal Start Condition: When SCL is HIGH and SDA jumps from HIGH to LOW, the data transmission starts. Stop Condition: When SCL is HIGH and SDA jumps from LOW to HIGH, the data transmission stops. Both the start condition and stop condition are issued by the master devices. After the start condition is generated, the bus is in an occupied state. And after the stop condition is generated, the bus is released and in an idle state. In an idle state, both SCL and SDA are at high levels. The process is shown in Figure 3 below. Figure 3 Start Condition and Stop Condition Acknowledgment signal: after the 1-byte transmission is completed, that is, within the 9th SCL clock cycle, the master needs to release the SDA bus and hand over the bus control to the slave. Due to the role of the pull-up resistor, the bus is at a high level at this time. If the slave correctly receives the data sent by the master, it will pull the SDA down, indicating an acknowledgment signal. Not acknowledgment signal: When the 9th SCL clock cycle is reached, the SDA remains high, indicating a not acknowledge signal. Each byte must be guaranteed to be 8 bits. When transmitting data, the highest bit (MSB) is transmitted first, and each transmitted byte must be followed by an acknowledgment bit (i.e. a frame has a total of 9 bits). If there is a not acknowledgment signal from the slave within a certain time, it is automatically considered that the slave has received the data correctly, and the master sends a stop condition to end the communication. The data transmission format is shown in Figure 4. Figure 4 Data Transmission Format I2C is usually used for communication between MCU peripherals or multiple MCUs. The I2C interface has the characteristics of simple hardware and easy software programming. What Is Analog to...

Broadcast Interval The broadcast interval is the time in which the application is "advertising" the BLE data. The settable value is from 20 ms to 1024 ms. The maximum value of broadcast interval of RF-star modules is 5 s. Because the broadcast interval is the main factor affecting the power consumption. The bigger the broadcast interval, the lower the power consumption.  However, if the module enables a bigger broadcast interval, the connection establishment and the scan operation will work slowly. Under the broadcast interval of 5 s, there may be no connection that can be built. RF-star recommends the maximum broadcast interval is 2 s. Connection Interval The connection interval is the time between two data transfer events (BLE connection events) between the central and peripheral device. The settable value is from 8 ms to 425 s. The default connection interval between RF-star modules is 20 ms. The connection interval between the BLE module and mobile phone will be different. The default minimum connection interval of the iOS system is 30 ms, and Andriod can reach 20 ms or less.

There are 2 types of flow control: hardware and software (Xon/Xoff or DC1/DC3). Hardware flow control uses dedicated signal wires such as RTS/CTS or DTR/DSR while software flow control signals by sending DC1 or DC3 control bytes in the normal data wires. Hardware Flow Control: List of RF-star BLE Modules Based on Nordic Semiconductor SoC: nRF52832: RF-BM-ND04, RF-BM-ND04I, RF-BM-ND08 nRF52810: RF-BM-ND04C, RF-BM-ND04CI, RF-BM-ND08C nRF52805: RF-BM-ND09, RF-BM-ND09A nRF52811: RF-BM-ND04A, RF-BM-ND08A nRF52833: RF-BM-ND07 nRF52840: RF-BM-ND05, RF-BM-ND05I, RF-BM-ND06 List of RF-star Modules Based on Silicon Labs SoC: EFR32BG22C112: RF-BM-BG22A1 EFR32BG22C224: RF-BM-BG22A3 Software Flow Control: RF-star Series Modules: RS02A1-A: RSBRS02AA, RSBRS02AI RS02A1-B: RSBRS02ABR, RSBRS02ABRI TI Series Modules: CC2640R2FRSM: RF-BM-4044B1, RF-BM-4044B2, RF-BM-4044B4, RF-BM-4044B5 CC2640R2FRGZ: RF-BM-4077B1 CC2640R2F-Q1: RF-BM-4077B2 CC2640R2LRHB: RF-BM-4055B1L CC2640R2LRGZ: RF-BM-4077B1L In order to make sure the normal receiving and transmitting function of the BLE modules, the hardware flow control must care about the CTS pin, while the software flow control must care about BRTS.

What is MTU (Maximum Transmission Unit)? MTU is the maximum transmission unit during the BLE data transmission. MTU is set to limit the maximum data length of BLE devices. The MTU of BLE4.0 is 23 bytes and BLE5.0 is 251 bytes. For BLE4.0, the maximum data package should be (MTU-3) bytes, that is, the data length should be 20 bytes at most. For BLE4.2, the communication rate is increased according to the raise of the MTU. For BLE5.0, MTU will be different from the SDK of different manufacturers.  Nordic nRF52 series: 247 bytes;  RF-star RS02Ax series: 251 bytes;  SiliconLabs EFR32BG22 series: 250 bytes;  TI CC26XX series: 251 bytes. Different mobile phone systems have different MTU. Android is 251 bytes, while iOS is 185 bytes. Each BLE packet is (MTU-3) bytes. For RF-star serial port module, the transparent transmission rate is one of the most important factors that the users will take into consideration. So, how can we achieve the biggest transparent transmission rate? The connection status of the BLE serial port module is the periodic operation of sleep events and connection events. The time between two events is the connection interval. The data only can be sent out when the connection event comes. There is no chance to send out the data during the sleep event. The smaller the connection interval, the closer the connection events. Then, more opportunities to send data and more data is sent. At most 6~7 frames of data can be sent during each connection event. So, when more data can be sent in one frame of data, more data can be transmitted during one connection event. One frame of data means the MTU. The bigger MTU, the higher the transparent transmission rate. When we test the limit transparent transmission rate, we usually shorten the connection interval and increase the MTU. What’s more, there are so many other factors that can influence the rate, including baud rate, single sending interval of serial port data.

What Are Authentication and Pairing Function of BLE Module? From the protocol perspective: Authentication: The authentication is used for checking device identity by UART data, which is only effective for APP. How to use the authentication function? Enable the authentication function and set a password for authentication for the slave device. When the master connects to the slave, the master must send the pre-set password in the authentication channel. After the slave receives the password, it will check whether the password is the same as the pre-set one. If yes, the connection will be kept if no, the connection will be disabled. Pairing: The pairing is supported by the Bluetooth underlying protocol. It will save the paired device in the pairing list. No matter what device for the master part is: a module or a mobile phone, it supports the paring function. From the function perspective: Authentication: The authentication requires the password in the channel for each connection. Pairing: The pairing supports the direct connection without a password after the first pairing is set. Only the MAC address of the pre-pairing device is deleted in the pairing list, there will be a password needed to set the connection again.

Basic Wiring of Bluetooth Module Pins are listed below: RF-star series module: RS02A1-A: RSBRS02AA, RSBRS02AI RS02A1-B: RSBRS02ABR, RSBRS02ABRI The pins need to be connected during transparent transmission test and debug: VCC, GND, TX, RX, BRTS, BCTS, EN (Active low for BRTS, BCTS and EN pins). The pins need to be connected during broadcasting: VCC, GND, EN. The pins need to be connected during flashing firmware (by J-Link or offline writer): SWC, SWD, VCC, GND, RES. TI series module: CC2540: RF-BM-S01, RF-BM-S02, RF-BM-S02I CC2541: RF-CC2540A1, RF-BM-S01A, RF-BM-S02A, RF-BMPA-2541B1 CC2640R2FRSM: RF-BM-4044B1, RF-BM-4044B2, RF-BM-4044B4, RF-BM-4044B5 CC2640R2FRGZ: RF-BM-4077B1 CC2640R2F-Q1: RF-BM-4077B2 CC2640R2LRHB: RF-BM-4055B1L CC2640R2LRGZ: RF-BM-4077B1L The pins need to be connected during transparent transmission test and debug: VCC, GND, TX, RX, RES, BRTS, BCTS, EN (Active low for BRTS, BCTS and EN pins). The pins need to be connected during flashing firmware: CC2540/CC2541: TDI, TDO (by CC-Debugger) CC2640: TMS, TCK (by XDS110) Nordic series module, Siliconlabs series module, TI CC26X2 series module: Nordic series modules: nRF52832: RF-BM-ND04, RF-BM-ND04I, RF-BM-ND08 nRF52810: RF-BM-ND04C, RF-BM-ND04CI, RF-BM-ND08C nRF52805: RF-BM-ND09, RF-BM-ND09A nRF52811: RF-BM-ND04A, RF-BM-ND08A nRF52833: RF-BM-ND07 nRF52840: RF-BM-ND05, RF-BM-ND05I, RF-BM-ND06 Silicon Labs series modules EFR32BG22C112: RF-BM-BG22A1 EFR32BG22C224: RF-BM-BG22A3 TI series modules: CC2642R: RF-BM-2642B1 CC2652R: RF-BM-2652B1 The pins need to be connected during transparent transmission test and debug: VCC, GND, TX, RX, RES, RTS, CTS (Active low for RTS and CTS). The pins need to be connected during broadcasting (Beacon): VCC, GND. The pins need to be connected during flashing firmware (by J-Link): SWC, SWD, VCC, GND, RES. Summary: Because each module has different definitions of BRTS, BCTS and CTS, RTS, it is recommended to connect those pins to avoid the problem that may be caused during the transparent transmission. Some of RF-star BLE modules (a few modules do not) have a sleep status indicator pin and a connection status indicator pin. Those pins are used to know the current Bluetooth module status or use an LED to indicate the current Bluetooth status through MCU.

What's difference between serial module and direct-driven module? The serial module is to forward data. And the direct-driven module can directly control peripheral circuits. The serial module is the bridge between the connected devices and the mobile devices, which enables two-way communication. The direct-driven module can be regarded as the CPU, the customer only needs to do the programming to drive the peripheral circuits. There are some direct-driven modules in RF-star. RF-star series modules: RS02A1-A: RSBRS02AA, RSBRS02AI RS02A1-B: RSBRS02ABR, RSBRS02ABRI TI series modules: CC2540: RF-BM-S01, RF-BM-S02, RF-BM-S02I CC2541: RF-CC2540A1, RF-BM-S01A, RF-BM-S02A

UartAssist serves as a powerful serial port debugging assistant with strong practicability. It supports the commonly used 110-115200bps baud rate. The debugging UART tool also allows customization of port number, parity, data bits, and stop bits. Moreover, The UART assistant is bilingual, supporting both Chinese and English, and seamlessly adjusts to the language settings of the operating system. Recommendation: A handy serial port assistant for mobile phone. No need for a heavy laptop when debugging on the go. It also supports TCP/IP debugging. Download the debugging UART tool here. There are some questions and answers on UART Assistant, which may help you a lot. 1. Please choose and click RTS and CTS on the UART Assistant (called DTR as well). For example: 2. Almost all of the RF-star BLE modules have the feedback string after power-on. If the module doesn’t have any string printed out after power on, pls try to reset the module or re-power on the module. If the above operations are done and there is no string shown, please check whether you choose the right UART port, because there may several UART ports working at the same time. 3. If the string is messy, please check whether you choose the right baud rate. 4. Dring using AT commands, please note whether the module needs the CRLF at the end of the AT commands. RF-star series and some of TI series modules do not need CRLF. RF-star series modules: RS02A1-A: RSBRS02AA, RSBRS02AI RS02A1-B: RSBRS02ABR, RSBRS02ABRI TI series modules: CC2640R2FRSM: RF-BM-4044B1, RF-BM-4044B2, RF-BM-4044B4, RF-BM-4044B5 CC2640R2FRGZ: RF-BM-4077B1 CC2640R2F-Q1: RF-BM-4077B2 CC2640R2LRHB: RF-BM-4055B1L CC2640R2LRGZ: RF-BM-4077B1L Nordic series, Silicon Labs series and some of TI series modules need to use “+++” to enter the AT command mode. All the AT commands need to be followed by a CFRL, then the modules can work normally. Under AT command mode, the module only can receive the data, but cannot send the data. If you would like to do the data transparent transmission, pls exit AT command mode at first. Nordic series modules: nRF52832: RF-BM-ND04, RF-BM-ND04I, RF-BM-ND08 nRF52810: RF-BM-ND04C, RF-BM-ND04CI, RF-BM-ND08C nRF52805: RF-BM-ND09, RF-BM-ND09A nRF52811: RF-BM-ND04A, RF-BM-ND08A nRF52833: RF-BM-ND07 nRF52840: RF-BM-ND05, RF-BM-ND05I, RF-BM-ND06 Silicon Labs series modules: EFR32BG22C112: RF-BM-BG22A1 EFR32BG22C224: RF-BM-BG22A3 TI series modules: CC2642R: RF-BM-2642B1 CC2652R: RF-BM-2652B1

What is an OTA update (over-the-air update)? An over-the-air (OTA) update is the wireless delivery of new software, firmware or other data to mobile devices. Which BLE modules do they have OTA function? Here is the list of BLE modules with OTA function. a) RF-star-based modules: RS02A1-A, RS02A1-B RS02A1-A: RSBRS02AA, RSBRS02AI RS02A1-B: RSBRS02ABR, RSBRS02ABRI APP: RF-star OTA. Support batch upgrading. Contact us at info@szrfstar.com. b) Silicon Labs-based modules: EFR32BG22 series: EFR32BG22C112: RF-BM-BG22A1 EFR32BG22C224: RF-BM-BG22A3 APP: EFR Connect c) Nordic Semiconductor-based modules: nRF52810, nRF52832, nRF52840, nRF52811, nRF52833 and nRF52805: nRF52832: RF-BM-ND04, RF-BM-ND04I, RF-BM-ND08 nRF52810: RF-BM-ND04C, RF-BM-ND04CI, RF-BM-ND08C nRF52805: RF-BM-ND09, RF-BM-ND09A nRF52811: RF-BM-ND04A, RF-BM-ND08A nRF52833: RF-BM-ND07 nRF52840: RF-BM-ND05, RF-BM-ND05I, RF-BM-ND06 APP: nRF Connect d) TI-based modules: CC2642R, CC2652R CC2642R: RF-BM-2642B1 CC2652R: RF-BM-2652B1 TIPS: Due to different SDKs, even the module is the same one, it cannot be upgraded. They can only upgrade iteratively on the original firmware.