CAN-bus adapter based CH372 System

Abstract: This paper introduces a new USB interface chip CH372 based on the CAN bus network adapter system design, a CAN bus using the USB interface connected to the computer network program. Using chip CH372 can not understand the agreement or any USB firmware or driver's case, to easily upgrade to the parallel port or USB interface, serial products. The system in the industrial field than in the past of the Ji Tong, can be more flexible, fast and efficiently a large amount of data exchange, and can be applied a variety of control systems of the Force, with good result Jia Zhi.

Introduction

Implementation of Fieldbus network technology combined with computer needs. At present, the expansion of computer equipment commonly used CAN bus interface, PCI bus or RS-232 bus. Although still a high-speed PCI computer peripheral interface with the main channel, but its main drawback is the limited take up system resources, expansion slot address; interruption of limited resources; and the plug is not convenient; more expensive; and design complexity, the need for high the quality of drivers, the system stability; and can not be used for portable computer expansion; RS-232 plug though convenient, but the transfer rate is too slow.

This design idea is to use the USB interface chip CH372, CAN network control computer and each node parameters quickly and accurately transfer. CH372 is a kind of generic USB bus interface chip, the computer system, by CH372 supporting software provide concise and easy to use Caozuo interfaces, Congershiqi and Bende side of the MCU communication on the hard drive as read and write in the Wenjianyiyang Jian Dan, You Yu CH372 shield the USB communication in all protocols, thus the computer application layer and a local-end connectivity between controllers, USB without the need to understand any agreement or firmware program or the driver situation, can easily parallel port, serial port products to upgrade to USB.

CAN bus and USB adapter to complete the data exchange between the CAN bus. Overall arrangements for data using the MCU USB bus and CAN bus data exchange between. MCU can be bounded by the hardware is divided into two parts: First, MCU and the USB bus to exchange data; 2 yes MCU control CAN controller, complete CAN data packet to the CAN bus bit serial protocol explained that the system structure shown in Figure 1.

CAN-bus adapter based CH372 System

Figure 1

Hardware Design

USB interface circuit in the micro-controller and USB interface, the choice of two ways: one is the use of USB communication with the microprocessor. With the increasingly wide range of USB applications, Intel, Cypress, Philips and other chip makers have introduced a USB communication interface of the microprocessor, such as 8X930A, 8X931A, EZ-USB and so on. These microprocessors have a USB interface, they are not compatible with previous development system need to purchase a new development system, the higher investment. The other is the ordinary microprocessor with a dedicated USB communications chip.

ASIC is now the more popular are USBN9602, SL11, PDIUSBD12 so. However, USB interface, the development of general requirements for designers of USB standard, Firmware and driver development, and so programmers are more in-depth understanding, thus limiting the general hardware engineers to use USB interface to product development. The system uses the USB interface chip CH372, using very simple, as long as the developers are familiar with microcontroller programming and simple VB or VC application programming, in a short period of time can develop the appropriate USB products.

CH372 is a common USB bus interface chip equipment, comply with USB1.1 protocol. Locally, CH372 with 8-bit data bus and read, write, chip select control lines and the interrupt output can be easily attached to the MCU, DSP and other controllers on the system bus; in the computer system, CH372 supporting software to provide a simple-to-use user interface, and a local microcontroller communication just as hard to read and write files. CH372 built-in USB communications in the underlying protocol, with built-in firmware mode and external firmware mode. In the built-in firmware mode, CH372 mask the USB communication to all agreements, and a local computer application layer to provide end to end connection between the controller. Use CH372, do not understand the USB protocol, or any firmware or even the driver, you can easily parallel port, serial port products to upgrade to USB.

CH372 chip's RD and WR are connected to the microcontroller can read and write strobe output pin strobe output pin. CS driven by the address decoding circuit for microcontroller with many peripheral devices as when equipment selection. INT can be connected to the microcontroller interrupt input pin is active low interrupt request. When CS and RD and A0 are low, CH372 in the data output by D7 ~ D0; when CS and WR are low, and A0, D7 ~ D0 The data is written CH372 chip; when the CS and WR are low and A1 is high, D7 ~ D0 The data is written as a command code CH372 chip. CH372 chip UD and UD-pin should be connected directly to the USB bus. If security for chip resistor or inductor series with the insurance, then the AC and DC Equivalent series resistance should be within the 5Ω. CH372-chip built-in power-on reset circuit, under normal circumstances, do not need to reset externally. CH372 chip work required to provide external 12MHz clock signal. In general, the clock signal from the CH372 built-in inverter frequency stabilization by crystal oscillation. External circuit is only required between the X1 and X0 pins to connect a nominal frequency of 12MHz crystal, and were X1 and X0 pins to connect on a capacity of 30pF capacitance high-frequency oscillation. CH372 chip support 5V or 3.3V supply voltage supply voltage. When using 5V operating voltage, CH372 chip VCC pin input external 5V power supply, and, V3 pin should add a capacity of about 0.1μF power supply decoupling capacitor. When using 3.3V operating voltage, CH372 V3 chip and pin should be connected to VCC pin, while the external 3.3V power supply input, and connect with CH372 other circuit chip operating voltage can not exceed 3.3V. Interface circuit shown in Figure 2.
CAN bus interface circuit this in part by the CAN controller, CAN interface chip and coupler component. CAN controller to complete all the requirements of CAN communication protocol, CAN interface chip CAN controller and the physical bus is the interface between, and through the optocoupler will be sent to the CAN data bus, the interface circuit shown in Figure 3.

CAN-bus adapter based CH372 System

Figure 3

CAN bus controller's use of Philips SJA1000, supported by the company's PCA82C250 interface to drive through the optical isolation device 6N137 bus and the controller realized the isolation. SJA1000 is a stand-alone controller for automotive and general industrial environments, the from the software point of view, the operation of the SJA1000 MCU's access to external memory through Zhiling to complete, Suo Yi, SJA1000 can be considered as one kind of Kuozhan RAM , SJA1000 Peli mode with standard mode and the two applications. Standard is consistent with the CAN2.0A protocol standard, the receiver buffer of 64 bytes; Peli is consistent with the 2.0B standard, capable of handling extended data format, with the arbitration lost capture, code reading and other functions.

PCA82C250 CAN controller and the physical bus is the interface between the current value it has qualified to protect the receiver output level, to avoid short-circuit the anode and cathode to prevent output stage damage, PCA82C250CAN interface controller provides a bus driver to send and reception, high speed up to 1Mbps, has strong anti-interference ability.

In order to enhance anti-jamming capability, SJA1000 and 82C250 CAN bus transceiver uses two high-speed optical isolation between the device and the controller bus 6N137 achieve isolation, in order to avoid interference, improve reliability. CAN controller can choose from RX0, TX0 or RX1, TX1 receive and send data, when using RX0, TX0 work, shall RX1 received on a stable level. High-speed optocoupler 6N137 maximum speed of up to 10Mbps, it can use a state of isolation to ensure reliable high-speed systems.
Software Design

The design used in micro-controller P89C51RD2, it is advanced CMOS single-chip 8-bit microprocessor technology. Work in 6 clock mode, the speed is twice the standard 51 microcontroller, this time up to the maximum external crystal 20MHz. In addition, the models support the programming and IAP ISP programming. Software main program flow chart shown in Figure 4.

CAN-bus adapter based CH372 System

Figure 4

First to MCU, SJA1000 and USB initialization, initialization cycle after the system is in wait state, if interrupt generation, to enter the corresponding interrupt service routine, if the CAN bus with data uploaded into the CAN interrupt service routine is from the microprocessor to receive data from the SJA1000 buffer, write data buffer the microprocessor, and sign to return home, if the host computer has data to download, then transferred to USB interrupt service routine (lower machine interrupt service program flow shown in Figure 5 below), the microprocessor reads data from the USB buffer, into the buffer, and return home signs, receive data is read from the buffer starting data sent to USB bus, USB bus through the transmission to the host computer ( Next for Data Upload subroutine flow chart shown in Figure 6), sending data is the data read from the buffer to write SJA1000 buffer, read from the CAN node, this treatment allows the microprocessor in the implementation of completed only after the corresponding interrupt program reads the buffer, and then perform the appropriate procedures can be completed to receive or send upper and lower machine data exchange. For the computer application program, the computer loaded WINCHIPHEAD provided CH372 Universal driver, no longer consider the USB communication protocol, firmware, drivers, auto-configuration process and the underlying data transmission. Only need to provide a dynamic link library interface function with VB or VC can prepare your own application.

CAN-bus adapter based CH372 System

Figure 5

CAN-bus adapter based CH372 System

Figure 6

Conclusion

In summary, the system for the computer and direct communication between the CAN bus provides an effective way to meet the networking and interface technology, field bus network and explore new methods of computer interface, is very practical significance .