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What are the differences between CAN and RS485?

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banh

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I've used CAN, but never on RS485 before.
I found that RS485 is also based on differential signals like CAN, for noisy environment.

What are the differences between CAN and RS485?
 

IanP

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rs485 vs can

The CAN standard includes a physical layer and a data-link layer which defines a few different message types, arbitration rules for bus access, and methods for fault detection and fault confinement. The physical layer typically uses differential transmission on a twisted pair wire.

The RS-485 is only a physical layer interface. And even then, there is no specification for connectors. You are on your own with respect to the higher layer protocols ..
The need for additional protocols is clear when you consider that RS-485 allows for multiple nodes to connect to the same wire ..
Every node on the network can generally listen at the same time. However, only one node can talk at any given time. If more than one node attempts to talk at once, the message will be garbled.
So, a higher level protocol, such as MODBUS, for example, is necessary to ensure that every node will get a chance to talk and that its message will get through ungarbled.

MODBUS: https://www.stonel.com/FieldLink/pdfs/mbdesc.pdf

Regards,
IanP
 

    banh

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banh

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can vs rs-485

besides this higher layer protocol such as MODBUS, what are the other protocols often used?

so, actually when using MODBUS, besides the RS485 transceiver, i need another driver IC for modbus? or is MODBUS can be purely software?
 

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rs485 and can physical layer shorting detection

MODBUS is just software platform (protocol) ..
The hardware platform in this case is the differential RS-485 ..

Here is a link to "Modbus Protocol Reference Guide:
https://www.eecs.umich.edu/~modbus/documents/PI_MBUS_300.pdf

Other software protocol, which uses the RS-485 as its hardware platform, however not as popular as the MODBUS, and used mostly in power management, is CBUS ..
Here you can find short description of CBUS:
https://www.integrate-oz.net/downlds/cbus.pdf

Regards,
IanP
 

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