User manual

MCP2515 CAN Bus Monitor Demo Board User’s Guide

2.4 FUNCTIONAL OPERATION

The MCP2515 CAN Bus Monitor Demo Board is basically a USB-to-CAN board which

provides visual feedback of Controller Area Network operation. The two boards

included in the kit can be used together to create a 2-node CAN bus.

The function of the board is determined by how it is powered.

2.4.1 Bus Monitor (Sniffer) Configuration

The board is a designated as a Bus Monitor when the board detects a connection to

the USB power (and enumerates to USB).

By default, this node is configured for 125 kb/s and the receive buffers are wide open

(i.e., will receive all messages on the bus). The PC software communicates with this

node.

2.4.2 Traffic Generator Configuration

The board is designated as a Traffic Generator when it is powered by a source other

than USB (In this case, the other board is being powered by the CAN cable). In this

configuration, the node responds to pressing the traffic generator button. Each

depression of the button increments the bus load to the next step until it rolls arount to

zero again, at which time, the load will increment again for every depression.

2.4.3 Headers/Test Points

Two of the headers are connected to the MCP2515 pins so the pins can be monitored.

The SPI and CAN serial interfaces, interrupt pin(s), and SOF pin are routed to head-

ers/test points.

The ICSP signals from the PIC18F4550 are routed to a header.

Note: The silkscreen on the board indicates that the bus loading ranges from 25%

to 100% when pressing the “LOAD” button. While the node can handle

these loads, the display in the Output window becomes meaningless at

loads above 5% - 8%. Therefore, the bus loading is reduced for demonstra-

tion purposes. The firmware can be modified to increase the traffic as

needed.