Microcontroller with LIN Bus Asynchronous Transceiver/Receiver Unit (UART)

“As automotive components continue to become more Electronic, automotive engineers are actively seeking solutions for advanced control and interface technology in vehicle systems. Currently, the space and energy available to embed these functional units in automotive systems is very limited. Due to its relatively low cost, the LIN bus is being widely used in distributed electrical control systems in automobiles, such as controlling power windows, adjusting stepper motors and DC power supplies in rearview mirrors and headlights, or managing Information collected by sensors about air temperature or seat location, etc.

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As automotive components continue to become more electronic, automotive engineers are actively seeking solutions for advanced control and interface technology in vehicle systems. Currently, the space and energy available to embed these functional units in automotive systems is very limited. Due to its relatively low cost, the LIN bus is being widely used in distributed electrical control systems in automobiles, such as controlling power windows, adjusting stepper motors and DC power supplies in rearview mirrors and headlights, or managing Information collected by sensors about air temperature or seat location, etc. The LIN bus transmits bytes up to 20kbps. Based on the structure of single master node and multiple slave nodes, usually, slave nodes are installed around transceivers, microcontrollers, sensor interfaces, or excitation drivers composed of discrete components.

Automotive engineers are using novel high-voltage mixed-signal technology to integrate complex – as yet incompatible component functions onto a single chip. Complex digital circuits (such as sensors), embedded microprocessors, and power circuits (such as excitation sources or switch drivers) can now be integrated using I3T high-voltage technology that is compatible with the 42V vehicle voltage.

Recently, a microcontroller with LIN bus asynchronous transceiver (UART) has been developed, which can be integrated with other slave node modules (such as LIN bus transceiver, voltage regulator, watchdog timer, etc.). , excitation driver and sensor interface) accessories are used together. At present, AMI semiconductor (AMIS) uses mixed-signal technology to integrate all the key slave node modules on a chip with specific functions, low power consumption, and standard IP modules, which pushes the development of LIN bus a step further.

AMI Semiconductor’s I3T80 is an 80V power supply intelligent module integration technology based on 0.35mmCMOS process. Meet the harsh operating conditions of 42V automotive systems. Devices developed from this technology include motor control drives, DC-DC converters, high-precision analog circuits with bandwidth filters, and ADCs and DACs. And I3T80 can embed and integrate a total of more than 150,000 gate circuits, and its communication protocol modules include PLL, USB, bus protocol controller, CAN and LIN communication controllers. In addition to this, it also provides ROM and RAM memory.

With the increasing number of electronic components in new automotive electronic applications, automotive designers are looking for a rational solution. In this way, high-integration, high-reliability SoC solutions emerge as the times require. The technical requirements of this solution can simplify the implementation steps and reduce the cost of control and interface with different electronic systems. AMIS’s high-voltage, mixed-signal technology meets this need. It combines semiconductor solutions with dedicated IP modules to meet any standard interface communication bus (LIN, CAN) node application and is compatible with 42V voltage level solutions.

The AMIS solution provides all the main functional modules required by the application layer and the data link layer. These functional modules can be programmed with VHDL code and evaluated with the AMIS development board, and they will be briefly introduced below. The module acquires the signal from the receiver and streams the resulting data through a digital filter to remove spurious transmissions that may be caused by the attenuation of the LIN bus signal. Therefore, the module improves the performance of the LIN protocol in harsh environments and minimizes synchronization and data sampling problems.

The Synchronizer module extracts the required information from the synchronization domain to determine the exact sampling rate of the encoder and decoder. The module features an internal crystal oscillator and employs a technique that minimizes the occasional rounding/rounding errors that occur in traditional UART technology. The main advantage of a synchronous machine is that it can execute the LIN protocol with a lower clock frequency. For example, a 250KHz master clock and 15% tolerance can be used to obtain accurate and error-free communication. In addition, the scheme of AMIS realizes a large variation range of duty ratio. A typical UART can achieve a duty cycle change between 33 and 66% with zero crystal error. However, using the AMIS solution can achieve a duty cycle variation between 12% and 88%, and can fully accommodate crystal errors. While providing a larger tolerance for the physical layer parameters, it also improves the electromagnetic compatibility which has a greater impact on the duty cycle.

The master node issues different slave instruction identifiers according to needs at the initial stage of system operation and during the operation process. For this purpose, the slave node must contain a certain number of registers. The ROM instruction number array refers to the different instructions executed in the slave node, with corresponding identifiers in RAM or EEPROM. The address register module identifies different slave nodes on the same LIN bus, and the second ROM array identifies different slave nodes for different applications and implementations. The identifier filter determines whether the instruction is executed or not according to the assigned identifier. If the identifier exists in the queue, the instruction is executed, otherwise it is not executed.

The error recognition module is in the data link layer, while the error correction is performed in the application layer. Therefore, the amount of error is defined in software by the embedded microcontroller. The error correction module in the application layer contains a status register, each error has a corresponding error flag, and the flag generates an interrupt request to the core of the microprocessor. Error flags can be cleared by reading the status register. Each error directly interrupts communication, causing a bit error to stop sending bytes. Then this frame information is ignored, and the slave node waits for the next interrupt field.

Frame buffers are another way to minimize interrupts to the microprocessor core. It works in conjunction with an identifier filter to reduce the number of interruptions to once per frame. The buffer contains 17 bytes (one identifier, eight transmit bytes, eight receive bytes).

AMIS provides different kernels as required. The core and the LIN controller are connected through interrupt signals and special function registers (SFRs). The LIN controller can be regarded as a peripheral device on the SFR bus. In addition to these LIN bus features, like similar semiconductor processing technology platforms, AMIS has developed an extensive library of IP blocks, including II (2) and SARADC blocks, time-delay triggers with output currents up to 0.3A, and HMIs with output currents up to 3A. bridge. Of course, utilizing slave nodes is only part of the overall functionality, and providing them with enough power to integrate them in today’s cars is the next big challenge for automotive electrical engineers.

In an ideal automotive power scheme, the power level would be converted from the traditional 12V battery voltage to a 42V power system. In the 42V system, the power level will continue to rise. For example, the maximum operating voltage in the entire life cycle of the system is set at 50V, and if there is a maximum dynamic overvoltage of 8V, the power supply voltage will reach 58V. Adding a 12V external drive load pump will make the voltage requirement of the system reach 70V, and adding an ESD protection window, the system voltage will reach 80V. And automotive semiconductor devices not only have to withstand higher voltages, but also must have sufficient robustness to meet their harsh operating environments, such as operating temperatures ranging from -40°C to +200°C. So far, the need to withstand higher voltages and meet harsh operating conditions has been a major obstacle to the application of smart SoC technology in 42V automotive electronic systems.