Design of hardware platform for special motion controller based on embedded system

1 Introduction

With the rapid development of embedded technology, it has been widely used in the field of industrial control. Therefore, it is of great significance to combine embedded technology with motion control technology to develop a high-speed and high-precision embedded motion controller. This paper designs a hardware platform for multi-input and multi-output dedicated motion controller with TMS320VC5402 as the core processor. The platform can realize multi-sensor signal acquisition, information fusion, position control algorithm, network function, multi-channel output to the drive system, and realize information/energy conversion.

2 Motion Controller Platform Hardware Design

2.1 Motion controller system hardware structure

According to the requirements of the motion controller interface, the system is divided into two parts: the main circuit and the peripherals. The main circuit part is composed of a digital circuit based on TI's processor chip TMS320VC5402; the peripheral part is composed of related peripheral interface circuits. According to different functions, it can be divided into the following modules: DSP minimum system, network card interface circuit, PCI interface, serial port transceiver circuit, analog quantity, pulse quantity and switch quantity interface, and human-computer interaction interface.

2.2 Introduction to each functional module of the hardware system

2.2.1 DSP independent small system interface circuit

The so-called minimum system refers to the simplest system that enables the DSP to operate normally under the condition of as few external components and circuits as possible. This system uses the 16-bit fixed-point DSP TMS320VC5402 as the core device to form the control core of the entire system. Since the selected TMS320VC5402 has a memory that can be used for data and program space, the minimum system can be composed of the DSP itself, the crystal oscillator, the reset circuit, the decoding circuit, etc.

2.2.2 Ethernet communication interface circuit design

One of the most important functions of motion controller based on embedded system is to realize network information transmission. Therefore, a network interface chip is needed to realize communication between networks. In this system, the RTL8019AS network interface chip of REALTEK company is used.

The RTL8019AS pins can be divided into power and clock pins, network media interface pins, bootstrap ROM and initialization EEPROM interface pins, main processor interface pins, output indication and working mode configuration pins. Therefore, the network card hardware interface circuit design is mainly divided into two parts: the first part is the realization of the network card and DSP interface, and the second part is the peripheral circuit design of the network card chip. The bus interface of RTL8019AS is compatible with the ISA bus. Although it cannot be directly interfaced with the external bus of 5402, it only needs some simple logic transformation. In addition, the pin levels of 5402 and RTL8019AS are incompatible, so the corresponding pins between them cannot be directly connected. It is necessary to add a level conversion chip in the middle. The CPLD in the system can complete the level conversion function, and the control logic signal of RTL8019AS can also be generated through CPLD.

2.2.3 PCI interface design

Since the system has high requirements for data transmission speed and real-time performance, one of the methods adopted is to communicate with the host through the PCI local bus. This has advantages over the traditional method of communicating through the ISA bus, such as high speed, plug-and-play, and good portability. In this system, TI's dedicated supporting chip PCI2040 is used to connect the PCI bus with the HPI (Host Port Interface) interface of DSP5402.

Figure 1 Motion controller hardware block diagram

Figure 2 AD conversion interface circuit diagram Figure 3 DA conversion interface circuit diagram

2.2.4 RS-422A serial port design

RS422A is a standard for balanced transmission, which can be sent and received at both ends. The transmitting end and the receiving end use balanced transmission and differential reception respectively. The former converts the logic level into a potential difference to complete the initial information transmission; the latter converts the potential difference into a logic level to complete the terminal information reception. RS422A uses two-wire transmission, which greatly improves the anti-interference ability. The maximum transmission rate can reach 10 Mb/s (when the transmission distance is 15 m). When the transmission rate drops to 90 kb/s, the maximum transmission distance can reach 1200 m, which can fully meet the remote requirements of the system.

The selection of RS422 communication interface chip needs to consider whether the communication rate of the chip meets the requirements. In the design, MAXIM's MAX3291 chip is selected. MAX3291 is a full-duplex, high-speed RS422 communication interface chip with output short-circuit protection and reception failure protection. It increases the distance and speed of reliable communication by reducing the internal signal interference caused by long lines. The communication speed can reach 5-10 Mbps. At the same time, it also allows up to 128 identical RS422 communication interface chips to be connected to the same bus, which provides convenience for multi-machine communication.

2.2.6 Implementation of D/A conversion interface

The D/A conversion chip uses TI's DAC7625UB. The interface hardware circuit of DAC7625UB and DSP is shown in Figure 3.
In the figure, VrefH and VrefL are the reference high voltage and reference low voltage of DA conversion, which indicates that the analog output changes between the two; CSDAC is the low level of the selection signal is valid; R/W is the read/write signal, the high level represents the processor sends a read command to DA, and the low level represents the send of a write command to DA; DA1-DA3 represents the 4-channel analog output interface used to indicate the completion of AD conversion; RST is the reset signal of DA, when the reset is valid, DA is in the initial state; LDAC is the enable signal of the processor loading DA. Similarly, these control and status signals of DA are connected to the I/O of CPLD, and the interface between processor and DA can be realized by programming CPLD.

2.2.7 Switching and pulse quantity interface

The system provides 7 standard TTL level pulse input and output interfaces. Including 2 pulses with a falling edge of 20s; 2 pulses with periods of 20ms and 5ms respectively, 3V-5V differential pulse width of 10us-20us, and pulse rising edge of no more than 0.5us; 3 signals with a period of 1ms, 3V-5V differential pulse width of 10us-20us. At the same time, it is also necessary to process 14 DC +24V and 4 DC +27V switching quantities. This function can be realized by CPLD, and the system is scalable. Since the level of the pulse and switching interface part is different from the level provided by the system, the pulse quantity needs to be isolated and converted, and the devices used are mainly photoelectric isolation and operational amplifiers.

The pulse quantity isolation conversion circuit is designed to measure the pulse quantity period, frequency and other values. The pulse quantity is electrically isolated through the high-speed photoelectric isolation device 6N137 to reduce interference, and then sent to the CPLD. By writing the corresponding hardware description language, the measurement of the pulse signal period and frequency is realized.

3 Experimental results and conclusions

After completing the hardware design of the motion controller, we used TI's integrated development environment CCS for development, and used the simulator to simulate and debug on the development target board. It is now running offline. Preliminary experiments show that the platform realizes the input and output of multiple analog quantities, pulse quantities, and switch quantities, and can communicate with other hosts in the network. Due to the powerful computing function of TMS320VC5402, it is easy to realize the information fusion of multi-sensor collected data and the corresponding position control algorithm.