MVI56-PDPS information transmission adopts CAN communication protocol, and the communication medium is twisted pair. Since the CAN bus is based on the encoding of sent messages and does not encode the CAN control nodes, the system is more expandable, while the addition or deletion of control nodes on the CAN bus will not have any effect on the remaining nodes of the system.

The MCU of the node controller can be a microprocessor with SPI interface or a microprocessor without SPI interface. The system uses a microprocessor without SPI interface, AT89C5l. AT89C51 can be directly connected to the SPI interface of the CAN controller through the P1 port and use software algorithms to implement the SPI interface protocol. the CAN bus transceiver TJAl050 acts as an interface between the MCP2510 and the physical bus. If the anti-interference capability of the system needs to be further improved, another opto-isolator can be added between MCP2510 and TJAl050.

In this paper, MCP2510 mainly takes the interrupt mode to receive and send bus data. The main sequence of the whole system provides two kinds of interrupts: timer interrupt and external interrupt. The interrupt subroutine of the timer interrupt is mainly responsible for processing the A/D data from analogue channels AINO to AIN7, sending the “data send request command” to the MCP25lO, and sending the data. The interrupt processing subroutine of the external interrupt mainly consists of the CAN bus error handling subroutine and the data receiving subroutine.