MCP2515 CAN Bus Monitor Demo Board User’s Guide
DS50001757B-page 16
2008-2014 Microchip Technology Inc.
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 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 kbps 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 con-
figuration, 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 around 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
headers/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 demonstration
purposes. The firmware can be modified to increase the traffic as needed.
