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Add link to can protocol

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Paul Guenette
2021-06-28 21:29:49 -04:00
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commit 70fcb98b83
2 changed files with 6 additions and 7 deletions
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docs/can-guide.md
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CAN is convenient for its simple and robust Physical Layer (PHY) that requires only a twisted pair of wires and a 120ohm termination resistor at each end. It has low jitter and low latency, because there is no host computer. It is relatively fast (CAN 2.0b supports 1 Mbps). Messages are easy to configure and load with data. Transceivers and controllers are inexpensive and widely available, thanks to its use in automotive.
## Hardware Setup
ODrive assumes the CAN PHY is a standard differential twisted pair in a linear bus configuration with 120 ohm termination resistance at each end. ODrive versions less than V3.5 include a soldered 120 ohm termination resistor, but ODrive versions V3.5 and greater implement a dip switch to toggle the termination. ODrive uses 3.3v as the high output, but conforms to the CAN PHY requirement of achieving a differential voltage > 1.5V to represent a "0". As such, it is compatible with standard 5V bus architectures.
## Setting up CAN on ODrive
CANSimple breaks the CAN Message ID into two parts: An axis ID and a command ID. By default, CAN is enabled on the ODrive, where Axis 0 has ID 0, and Axis 1 has ID 1. The ID of each axis should be unique; each should be set via `odrivetool` before connecting to the bus with the command:
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If your ODrive is the "last" (furthest) device on the bus, you can use the on-board 120 Ohm termination resistor by switching the DIP switch to "CAN 120R". Otherwise, add an external resistor.
### Verifying Communcation
By default, each ODrive axis will send a heartbeat message at 10Hz. We can confirm our ODrive communication is working by starting the `can0` interface, and then reading from it:
docs/can-protocol.md
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# CAN Protocol
## Hardware Setup
ODrive assumes the CAN PHY is a standard differential twisted pair in a linear bus configuration with 120 ohm termination resistance at each end. ODrive versions less than V3.5 include a soldered 120 ohm termination resistor, but ODrive versions V3.5 and greater implement a dip switch to toggle the termination. ODrive uses 3.3v as the high output, but conforms to the CAN PHY requirement of achieving a differential voltage > 1.5V to represent a "0". As such, it is compatible with standard 5V bus architectures.
This document describes teh CAN Protocol. For examples of usage, check out our [CAN Guide!](can-guide.md)
ODrive currently supports the following CAN baud rates:
* 125 kbps
* 250 kbps (default)
* 500 kbps
* 1000 kbps
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## Configuring ODrive for CAN