How the MCU works
MCU (Micro Control Unit) Chinese name is called the Micro Control Unit, also known as Single Chip Microcomputer (Single Chip Microcomputer) or Single Chip Microcomputer, is refers to with the emergence of large scale integrated circuit and its development, the computer CPU, RAM, ROM, timing counter and a variety of I/O interface integration within the same Chip, form the computer Chip level, do different combination Control for different applications.
MCU plays a key role in the modern popular video conference equipment, through the MCU device to the following terminal device set the permission attribute can form a complete video conference network.
MCU is the core part of video conference system, providing users with group meeting and multi-group meeting connection service.
At present, MCU of mainstream manufacturers can generally provide access service of up to 190 users for a single machine, and can be cascated. Mainstream manufacturers support three-level digital combination cascination (superior MCU can control subordinate MCU terminals, select the terminals, remote control camera and other meeting operations), which can basically meet user requirements.
The use and management of the MCU should not be too complex and should be accessible to the general staff of the customer's technical department or even the administration department.
The MCU is connected with the temperature sensor by I2C bus.
I2C bus occupies 2 MCU input and output lines, and the communication between them is completely completed by software.
The address of the temperature sensor can be set by 2 address pins, which allows 8 such sensors to be connected to an I2C bus at the same time.
In this scheme, the 7-bit address of the sensor has been set to 1001000.
When the MCU needs to access the sensor, it emits an 8-bit register pointer and then the sensor address (7-bit address, low order WR signal).
The sensor has three registers available to the MCU, and the 8-bit register pointer is used to determine which register the MCU will use.
In this scheme, the main program will constantly update the configuration register of the sensor, which makes the sensor work in a one-step mode, and the temperature will be measured every time it is updated.
To read the contents of the sensor measurement register, the MCU must first send the sensor address and register pointer.
The MCU sends a start signal, then emits the sensor address, and sets the RD/WR pin to a high level to read the measurement register.
In order to read out the 16-bit data in the sensor's measurement register, the MCU must communicate with the sensor twice in 8-bit data.
When the sensor is powered on, the default measuring accuracy is 9 bits and resolution is 0.5c /LSB (measuring range: -128.5c to 128.5c).
The default measurement accuracy is adopted in this scheme. The sensor can be reset as needed to improve the measurement accuracy to 12 bits.
If only general temperature indication is required, such as automatic thermostat, resolution up to 1 C will suffice.
In this case, the low 8-bit data of the sensor can be ignored, and only the high 8-bit data can meet the design requirements of resolution 1 C.
Since registers are read in the order of 8 bits higher followed by 8 bits lower, the lower 8 bits can be read or not.
The advantages of reading only high 8 bits of data are twofold. Firstly, it can shorten the working time of MCU and sensor and reduce power consumption.
The second one does not affect the resolution index.
After the MCU reads the sensor's measurements, the conversion is performed and the results are displayed on the LCD.
The whole process includes: judging the sign of the display result, converting the binary code to BCD code, and transferring the data to the relevant registers of LCD.
When the data is processed and the results are displayed, the MCU sends a one-step instruction to the sensor.
A single step tells the sensor to start a temperature test and then automatically go into wait mode until the analog-to-digital conversion is complete.
When MCU issues a single step instruction, it will enter LPM3 mode. At this time, the MCU system clock will continue to work, generating a timing interrupt to wake up the CPU.
The length of the timing can be programmed to suit the needs of specific applications.