Abstract: When designing a frequency converter using the latest DSP chip TMS320LF2407, since the chip's internal asynchronous serial port is already used for communication with the host computer, an additional asynchronous serial port must be added for communication with the keyboard. This paper uses the DSP's I/O port to expand the serial communication port for communication with the keyboard MCU, and presents the design methods for the communication protocol, hardware, and software. Keywords : DSP; frequency converter; communication [b]1 Introduction[/b] The latest DSP chip from TI, the TMS320LF2407, is a low-voltage power supply chip specifically designed for motor control. It is powerful, with a main clock frequency of up to 30MHz, and most instructions are completed in a single cycle. For motor control, the TMS320LF2407 also has a set of powerful peripheral devices: an SCI serial port, an SPI serial port, a watchdog timer, and two 6-channel PWM outputs, which can simultaneously perform controlled rectification and controlled inversion, realizing high-performance control of the motor by a single chip. When developing a frequency converter using the TMS320LF2407, the DSP chip only has one asynchronous serial port. An RS-485 interface has been used for communication between the frequency converter and the host computer. To monitor and control the frequency converter's operation using the keyboard, communication between the DSP and the keyboard MCU must be designed. For the communication between the frequency converter's DSP control board and the keyboard interface, we use the DSP's I/O ports to expand the serial port and designed the corresponding hardware and software. 2. Hardware Design The main control chip of the frequency converter is the TMS320LF2407, which mainly performs functions such as generating three-phase PWM signals and motor control. The frequency converter's keyboard MCU uses the AT2051 chip from Atmel, which mainly handles user key commands, parameter settings, and monitors the frequency converter's operating data. To improve the communication's anti-interference capability and achieve long-distance communication, RS-485 serial communication is used, with the TI 75179 chip used for the 485 communication. Since the TMS320LF2407 is a low-voltage powered DSP chip (3.3V), while the AT2051 and 75179 chips are powered (5V), the entire system is a hybrid power supply system. The inverter's 5V power supply is generated by the switching power supply on the inverter's power board, powering chips such as the AT2051 and 75179. TI's low-dropout power supply chip TPs7333 converts the 5V voltage to 3.3V to power the DSP. However, there is a communication signal level conversion issue between the DSP and the 75179 chip. An inexpensive optocoupler TLP521 is used to convert the communication signal level, changing the signal from DSP to 75179 from 3.3V to 5V. Simultaneously, the signal from 75179 to DSP is also converted from 5V to 3.3V, which fully meets the communication speed requirements at 4800 baud. [b][align=center]For more details, please click: Inverter DSP Control Board and Keyboard Communication Design[/align][/b]