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What Differential Voltages Correspond to High and Low Logic Levels in CAN Protocol?

Hardware: Digital I/O (DIO)

Problem:
I would like to acquire my CAN signals through a data acquisition board and to do so I need to know how to interpret the voltages on the differential lines (CAN_H and CAN_L) as logic levels high (dominant) and low (recessive).

Solution:
The CAN standard specifies that for logic low (recessive), CAN_L and CAN_H should be at Vcc/2.  For logic high (dominant), CAN_L is at 1.5V and CAN_H is at Vcc-0.9V.

This implies that for a Vcc of 5V, the following points are true:

• Logic LOW differential voltage between CAN_H and CAN_L is 0V (2.5V - 2.5V = 0V)
• Logic HIGH differential voltage between CAN_H and CAN_L is 2.6V (4.1V - 1.5V = 2.6V)

National Instruments also has devices specifically designed for handling the CAN protocol which interface to LabVIEW and C-based programming environments, which greatly simplifies working with CAN, as opposed to dealing with the raw bits. For more information on these products, please visit the "Controller Area Network (CAN) Product Page" linked below. Also, for more information on the CAN protocol in general, please visit the "Tutorial: Controller Area Network (CAN): Overview" link below.

Related Links:
Controller Area Network (CAN) Product Page

Tutorial: Controller Area Network (CAN) Overview


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Report Date: 03/20/2007
Last Updated: 03/21/2007
Document ID: 47JEJCZC

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