Minimum system design based on MSP430F149

O Introduction

A single-chip microcomputer chip combined with necessary external devices, generally including power supply and power switch, reset circuit, crystal oscillator, input and output circuits, can form a minimum system.

The MSP430F149 chip is an ultra-low power microprocessor launched by TI in the United States. It has 60KB+256 bytes of FLASH, 2KB RAM, including basic clock module, watchdog timer, 16-bit timer with 3 capture/compare registers and PWM output, 16-bit timer with 7 capture/compare registers and PWM output, 2 8-bit parallel ports with interrupt function, 4 8-bit parallel ports, analog comparator, 12-bit A/D converter, 2 serial communication interface modules. The MSP430F149 chip has the following features:

1) Low power consumption: When the voltage is 2.2V and the clock frequency is 1MHz, the active mode is 200μA; when the shutdown mode is only 0.1A, it has 5 energy-saving working modes.

2) High-efficiency 16-bit RISC-CPU, 27 instructions, 8MHz clock frequency, instruction cycle time is 125ns, most instructions are completed in one clock cycle; at 32kHz clock frequency, the execution speed of the 16-bit MSP430 microcontroller is higher than the execution speed of a typical 8-bit microcontroller at 20MHz clock frequency.

3) Low voltage power supply, wide operating voltage range: 1.8~3.6V;

4) Flexible clock system: two external clocks and one internal clock;

5) Low clock frequency enables high-speed communication;

6) With serial online programming capability;

7) Powerful interrupt function;

8) Short wake-up time, waking up from low power mode takes only 6μs;

9)ESD protection, strong anti-interference ability;

10) The operating environment temperature range is -40 to +85°C, suitable for industrial environments.

All peripheral modules of the MSP430 series microcontrollers are controlled through special registers, so the programming is relatively simple. During programming development, you can choose assembly or C language programming through a dedicated programmer. IAR has developed a dedicated C430 language for the MSP430 series microcontrollers, which can be directly compiled and debugged through WORKBENCH and C-SPY, which is flexible and easy to use.

1 Overall system design

The minimum system is composed of the basic circuits necessary to ensure the reliable operation of the processor, mainly including power supply circuit, clock circuit, reset circuit, communication interface circuit, and data storage circuit. Its hardware block diagram is shown in Figure 1.

1.1 Power supply circuit

This system requires +5V and +3.3V DC regulated power supplies, of which MSP430Fl49 and some peripheral devices require +3.3V power, and others require +5V power. In this system, +5V DC voltage is used as input voltage, and +3.3V is directly linearly stepped down from +5V. The power supply circuit principle is shown in Figure 2.

1.2 Crystal Oscillator Circuit

The clock module of the MSP430 series microcontroller includes three clock sources: digitally controlled oscillator (DCO), high-speed crystal oscillator and low-speed crystal oscillator. This is to solve the contradiction between the system's requirements for fast data processing and low power consumption. By designing multiple clock sources or designing various working modes for the clock, the clock requirements of real-time applications of certain peripheral components can be solved, such as low-frequency communication, LCD display, timer, counter, etc. The digitally controlled oscillator DCO has been integrated into the MSP430. In the system, only two circuits, high-speed crystal oscillator and low-speed crystal oscillator, need to be designed.

The low-speed crystal oscillator (LFXT1) meets the requirements of low power consumption and the use of a 32.768kHz crystal. The LFXT1 oscillator works in low-frequency mode by default, that is, 32.768kHz, and can also work in high-frequency mode by connecting an external 450kHz to 8MHz high-speed crystal oscillator or ceramic resonator. In this circuit, we use the low-frequency mode, and the crystal oscillator is connected to the MCU via XIN and XOUT with two 22pF capacitors.

The high-speed crystal oscillator is also called the second oscillator XT2. It provides the clock for the MSP430F149 when it works in high-frequency mode. The maximum frequency of XT2 can reach 8MHz. In the system, XT2 uses a 4MHz crystal. XT2 is connected to the MCU through XT2IN and XT2OUT with two 22pF capacitors. The principle is shown in Figure 3.

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1.3 Reset circuit schematic

Manual reset is a commonly used function in minimum systems. This system uses a dedicated reset chip IMP811 to implement manual reset. The principle is shown in Figure 4.

1.4 Communication interface circuit

The communication interface is responsible for exchanging data with the peripheral serial host and supporting printing and other tasks.

Serial communication only requires fewer ports to achieve intercommunication between microcontrollers and PCs, which has incomparable advantages. There are two modes of serial communication: asynchronous mode and synchronous mode. The MSP430 series has USART modules to implement serial communication. In this design, the USART0 module of MSP430F149 communicates with the peripheral serial host through the RS232 serial port.

The EIA-RS232 standard is a serial data transmission bus standard established by the Electronic Industries Association (EIA) of the United States. In the early days, it was used for long-distance data transmission between computers and terminals through telephone lines and modems. With the development of microcomputers and microcontrollers, this communication method is used not only for long distances but also for short distances. In short-distance communication systems, telephone lines and modems are no longer used, but end-to-end connections are made directly. The RS232 standard uses negative logic, and the standard logic "1" corresponds to -5V to -15V level, and the standard logic "0" corresponds to +5V to +15V level. Obviously, the signal level conversion must be performed for communication between the two.

This system is implemented using a dedicated level conversion chip MAX3232. The MAX3232 chip is a level conversion chip produced by MAXIM, which contains two receivers and drivers and has reliable performance. The principle is shown in Figure 5.

1.5 Data storage circuit

The data storage uses a large-capacity E2PROM CAT24WC256. It is a 256K-bit serial CMOS E2PROM, which contains 32768 bytes, each byte is 8 bits. CATALYST's advanced CMOS technology reduces the power consumption of the device. The CAT24WC256 has a 64-byte page write buffer. The device is operated through the I2C bus interface. The principle is shown in Figure 6.

2 Conclusion

The minimum system can be directly used as a core component in engineering and scientific research, and has good versatility and scalability. Based on the minimum system, secondary development and functional expansion can be easily carried out, which can shorten the development cycle and reduce development costs. This article implements the basic functions of the minimum system and introduces the hardware circuits of each module. The minimum system can be appropriately modified and applied to electronic design, computer teaching and scientific research, industrial control and other fields.