The ATmega 162 is an 8-bit microcontroller based on AVRRISC's low-power CMOS from ATMEL. By executing an instruction in one clock cycle, the ATmega 162 achieves performance close to 1 MIPS/MHz, allowing the juicer to strike a balance between power consumption and execution speed. The AVR core connects 32 general purpose working registers with a rich instruction set. All working registers are directly connected to the ALU arithmetic logic unit, allowing a single instruction to be executed in one clock cycle while accessing two separate registers. This structure improves code efficiency and gives AVR nearly 10 times better performance than a normal CISC microcontroller. This paper uses ATmega 162 to develop a keyboard-liquid crystal display, a two-phase DC brushless motor without position sensor and an asynchronous serial communication port to realize data acquisition and transmission. Experiments show that these systems developed with ATmega 162 have reliable performance, low cost, flexible software design, and rich hardware interface functions, which have created favorable conditions for future system upgrades.
2 ATmega162 structure and characteristics
The ATmega162 features 35 programmable I/O lines, 40-pin PDIP, 44-pin TQFP and 44-pin MLF. Four 8-bit bidirectional I/O ports A, B, C, D, a 3-position bidirectional I/O port with internal pull-up resistors. Each port has three corresponding I/O port registers, which are data register PORTx, direction register DDRx, and input pin register PINx. When DDxn is written to 0, the corresponding Pxn is configured as an input pin, and PORTxn is set. When 1, the internal pull-up resistor configured for this pin is active. When DDxn is 1, the corresponding Pxn is configured as an output pin, and the data in PORTxn is the output level of the external pin, which is 1, the port pin is forcibly driven high, and the output is high (output current); Clear PORTxn, the port pin is forced low, and the output is low (sink current). During the reset process, the port is a three-state port even if the system clock has not been started. It can also be used as an address/data multiplexer to provide many special interface functions of the ATmega162. Port C provides the functionality of the JTAG interface. The internal pull-up resistors for pins PC7 (TDD, PC5(TMS), and PC4(TCK) are always in active mode (including reset) while the JTAG interface is enabled.
ATmega162 has the following features: 16 kB in-line programming FLASH with literacy; 512 B E2PROM; 1 kB SRAM memory; 35 general purpose I/O ports; 1 external memory interface; 32 general working registers; JTAG interface for boundary scan function; support online compilation, programming and simulation debugging; support programming of FLASH, E2PROM, chip fuse and security lock bits; 4 flexible timer/counters with comparison mode, 2 with comparison Mode 8-bit timer/counter with prescaler, 2 prescalers, 16-bit timer/counter with compare and capture modes, real-time counter with independent oscillator; 6 PWM channels; internal and external Interrupt source; power-on reset and programmable voltage detection circuit; internal calibratable RC oscillator; 2 programmable UART interfaces; programmable watchdog timer with internal clock; SPI serial interface; BOOT area It has independent encryption bits, which can be read by the on-chip boot program during system programming and writing. It is fully readable; the on-chip execution time is 2 clock cycles. Hardware multiplier; and five kinds of software selectable power saving mode.
The ATmega 162 is manufactured using ATMEL's high-density non-volatile memory technology. On-chip FLASH can be programmed and self-programmed via the SPI interface + through the programmer, or through the JTAG interface, or using the self-booting BOOT program. The self-booting BOOT program allows the chip to download the application through any hardware serial communication interface during the working process and write it to the application area of ​​the FLASH (IAP). When updating the application area code of the FLASH, the self-booting program in the BOOT area of ​​the FLASH will continue to execute, realizing the function of simultaneous reading and writing. By integrating the enhanced RISC 8-bit CPU with a system-programmed and application-programmed FLASH memory on a single chip, the ATmega 162 is a powerful microcontroller that provides a flexible, low-cost solution for multiple embedded control applications.
2.1 Comparison of ATmega162 and other similar devices
The most mundane CPUs in the control field are just three types: 51 series, AVR series, and PIC series. ATMEL's new 90 series MCUs include high-speed flash memory FLASH, which is based on the RISC (Reduced Instruction Set CPU) structure, which is referred to as AVR MCU. Significant improvements have been made.
Since the main CPU in this design needs to calculate and convert the temperature data, the general 51 series CPU is very difficult to perform, and the animation of the stars flashing and the reading data of the LOADING are added to the graphic display, so It is also required that the main CPU has the advantages of extremely fast operation speed and program reproducibility. Therefore, after comparison of various schemes, it was decided to use ATmega162 in the AVR series as the main CPU. At the same time, ATmega162 has two serial communication ports, which can fully satisfy the communication with the computer.
2.2 Comparison of temperature detection devices
There are many ways to do temperature detection. It is more common to use an A/D converter and then connect a temperature sensor. Our conventional A/D sensor is 0809 (8-channel A/D converter), and the sensor can be used. According to the actual situation of the choice, the general selection principle is to meet the range of measurement temperature, accuracy and sensitivity. For this design, the temperature range to be measured is room temperature (0 to 100 ° C), the accuracy can be 1 ° C, and the sensitivity is about 1 s. So I did not use 0809 to do it, but chose an integrated chip commonly used for ambient temperature detection in the market - DS18B20, the package is TOP92, using a single bus to transfer data. From the cost point of view, the 18B20 is about 15 yuan, which is nearly half cheaper than the price of the AD0809, and it can also save the money to buy the sensor, of course, under the premise that the measurement requirements can be met.
3 ATmega162 design and application
According to the design task requirements, this design uses the ATmega162 in the AVR microcontroller as the main control CPU, uses the 89C2051 as the auxiliary CPU to collect the temperature value transmitted by the digital temperature sensor DS18B20, and transmits the temperature value to the ATmega162 through the connection of the 8-bit port. Realize the collection of multi-channel temperature values. Then through ATmega162 arithmetic processing, digital display of multi-channel temperature can be realized, and the corresponding temperature histogram can also be displayed.
ATmega162 can be simulated online and online. When online simulation is required, the TCK, TDO, TMS, and TDI pins of the emulator should be pulled up by 4.7 kΩ and connected to the corresponding pins of ATmega162. Then connect the NSRST of the emulator to the RST of the ATmega162, connect the VTRES of the emulator to the VCC of the ATmega162, and share the emulator with the ATmega162. When the program is simulated online, its program has been automatically solidified into the CPU, thus avoiding the problem of curing failure like 89C51. The system block diagram is shown in Figure 1.
Figure 1 system block diagram
3.1 ATmega162 and keyboard and LCD display design
In this design, the ATmega162 uses a 3.686 4 MHz external crystal. The reset mode uses power-on reset. The AVR has three reset modes (power-on reset, external reset, watchdog reset). Because of the unstable operating voltage, the reset circuit can be ensured only by power-on reset. The device will not start working until VCC reaches a safe level.
The keyboard is an indispensable input tool for various CPUs, through which he can input programs and data to realize man-machine dialogue. The keys of the keyboard are arranged in a matrix of 3×4, and the I/O lines PC1 to PC3 are input (set to 0) as the column scan line of the keyboard; PC4~PC7 are outputs (set to 1) as the line of the keyboard. Scan the line and pull up the resistor. When it is determined that there is a key press, the mechanical shake of the key is removed by time delay, and the position of the closed key is determined again. If a key is pressed, the key value is calculated and returned.
The 8-bit of the AT port of the ATmega162 is connected to the data terminal of the LCD screen, and the DDRA of the ATmega162 is set to 0xFF, so that the PA port can only be an output. The PB port is the control of the LCD screen. The PB0 is connected to the RS, the PB1 is connected to the RW, the PB2 is connected to the reset terminal RST, the PB3 is connected to the enable terminal E for enabling control, and the PB4 and PB5 are respectively selected from the liquid crystal screen. CSB, CSA connected. The PD port is connected to the P1 port of the 89C2051. As the input port of the temperature data, the DDRD is also 0x00, and PD1 and PD2 are connected as serial communication ports to the TIN1 and TIN2 of the MAX232 respectively. PE0 and PE1 are used as the output of the temperature sensor detection signal, and PE2 is used as the temperature detection completion signal, so the DDRE is 0x07.
In this design, the PA port of ATmega 162 is connected as the data terminal to DB0 to DB7 of the LCD screen. PB0 is connected to RS as the write state, PB1 is connected to RW to control the read state, PB2 is connected to RST as the LCD reset control, and PB3 is connected to E. It is used to control the enable end of the LCD screen. When the data and commands are correctly written to the LCD screen, the ATmega 162 sets PB3 to a high level and the LCD screen starts to execute the written program and calls the newly written data, PB4, PB5 and PB6 is connected to the CSA, CSB and CSC of the LCD screen respectively. They are selected as the chip selects of the middle, left and right display respectively, and are all active low. When you need to write on the middle screen, such as display data, ATmega 162 first sets PB4 low, then sets RS to high level, then pulls down RW voltage, then puts the data on PA port to make LCD screen Can receive, and finally open the enable E, so that a data transfer is completed. By inputting 32 cycles, you can input a 16×16 Chinese character into the LCD screen.
It is worth noting that when using the emulator, you must power on the AT-mega162 board before powering up the emulator, and then use AVR Studio for online emulation. Otherwise, it will not be properly connected.
When selecting the system clock source, the fuse bit should be correctly configured. The fuse bit determines the way the system uses the clock source. It cannot be changed during normal operation of the MCU. It should be based on the selected clock source form and wake-up mode before debugging. The fuse bit is properly configured in the emulation system to match the clock source to the fuse bit.
3.2 DS18B20 temperature sensor design
The DS18B20 uses a single bus method to transfer commands and data for temperature detection. This requires an absolutely accurate frequency for transmission. For 18B20, the accuracy of the instruction is microsecond, and if the AT-mega 162 is used. C language to write, the program is not so accurate, so this design added 89C2051, using assembly language to write 18B20 control program. The communication between the two CPUs is directly connected, because the AT-mega 162 can set the working direction of the port (determined by the DDR value).
The P1 port of the 89C2051 is connected to the PD port of the ATmega162 for data exchange. The P3.0 and P3.4 of the 89C2051 are connected to the PE0 and PE1 of the ATmega162 respectively as the control of the temperature acquisition of the 89C2051 by the ATmega162. The P3.7 of the 89C2051 is connected to the PE2 of the ATmega162 as the 89C2051 to issue a read data command to the ATmega162. In this design, multiple temperature sensors can be connected, only two are connected, and their data ports are connected to P3.1 and P3.5 of 89C2051.
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