FRC CAN Device Specifications

This document seeks to describe the basic functions of the current FRC® CAN system and the requirements for any new CAN devices seeking to work with the system.

Addressing

FRC CAN nodes assign arbitration IDs based on a pre-defined scheme that breaks the ID into 5 components:

Device Type

This is a 5-bit value describing the type of device being addressed. A table of currently assigned device types can be found below. If you wish to have a new device type assigned from the Reserved pool, please submit a request to FIRST.

Device Types
Broadcast Messages	0
Robot Controller	1
Motor Controller	2
Relay Controller	3
Gyro Sensor	4
Accelerometer	5
Ultrasonic Sensor	6
Gear Tooth Sensor	7
Power Distribution Module	8
Pneumatics Controller	9
Miscellaneous	10
IO Breakout	11
Reserved	12-30
Firmware Update	31

Manufacturer

This is an 8-bit value indicating the manufacturer of the CAN device. Currently assigned values can be found in the table below. If you wish to have a manufacturer ID assigned from the Reservedpool, please submit a request to FIRST.

Manufacturer
Broadcast	0
NI	1
Luminary Micro	2
DEKA	3
CTR Electronics	4
REV Robotics	5
Grapple	6
MindSensors	7
Team Use	8
Kauai Labs	9
Copperforge	10
Playing With Fusion	11
Studica	12
The Thrifty Bot	13
Redux Robotics	14
AndyMark	15
Vivid Hosting	16
Reserved	17-255

API/Message Identifier

The API or Message Identifier is a 10-bit value that identifies a particular command or message type. These identifiers are unique for each Manufacturer + Device Type combination (so an API identifier that may be a “Voltage Set” for a Luminary Micro Motor Controller may be a “Status Get” for a CTR Electronics Motor Controller or Current Get for a CTR Power Distribution Module).

The Message identifier is further broken down into 2 sub-fields: the 6-bit API Class and the 4-bit API Index.

API Class

The API Class is a 6-bit identifier for an API grouping. Similar messages are grouped into a single API Class. An example of the API Classes for the Jaguar Motor Controller is shown in the table below.

API Class
Voltage Control Mode	0
Speed Control Mode	1
Voltage Compensation Mode	2
Position Control Mode	3
Current Control Mode	4
Status	5
Periodic Status	6
Configuration	7
Ack	8

API Index

The API Index is a 4-bit identifier for a particular message within an API Class. An example of the API Index values for the Jaguar Motor Controller Speed Control API Class is shown in the table below.

API Index
Enable Control	0
Disable Control	1
Set Setpoint	2
P Constant	3
I Constant	4
D Constant	5
Set Reference	6
Trusted Enable	7
Trusted Set No Ack	8
Trusted Set Setpoint No Ack	10
Set Setpoint No Ack	11

Device Number

Device Number is a 6-bit quantity indicating the number of the device of a particular type. Devices should default to device ID 0 to match other components of the FRC Control System. Device 0x3F may be reserved for device specific broadcast messages.

Protected Frames

FRC CAN Nodes which implement actuator control capability (motor controllers, relays, pneumatics controllers, etc.) must implement a way to verify that the robot is enabled and that commands originate with the main robot controller (i.e. the roboRIO).

Broadcast Messages

Broadcast messages are messages sent to all nodes by setting the device type and manufacturer fields to 0. The API Class for broadcast messages is 0. The currently defined broadcast messages are shown in the table below:

Description
Disable	0
System Halt	1
System Reset	2
Device Assign	3
Device Query	4
Heartbeat	5
Sync	6
Update	7
Firmware Version	8
Enumerate	9
System Resume	10

Devices should disable immediately when receiving the Disable message (arbID 0). Implementation of other broadcast messages is optional.

Requirements for FRC CAN Nodes

For CAN Nodes to be accepted for use in the FRC System, they must:

Communicate using Arbitration IDs which match the prescribed FRC format:
- A valid, issued CAN Device Type (per Table 1 - CAN Device Types)
- A valid, issued Manufacturer ID (per Table 2 - CAN Manufacturer Codes)
- API Class(es) and Index(s) assigned and documented by the device manufacturer
- A user selectable device number if multiple units of the device type are intended to co-exist on the same network.
Support the minimum Broadcast message requirements as detailed in the Broadcast Messages section.
If controlling actuators, utilize a scheme to assure that the robot is issuing commands, is enabled, and is still present.
Provide software library support for LabVIEW, C++, and Java or arrange with FIRST® or FIRST’s Control System Partners to provide such interfaces.

Universal Heartbeat

The roboRIO provides a universal CAN heartbeat that any device on the bus can listen and react to. This heartbeat is sent every 20 ms. The heartbeat has a full CAN ID of 0x01011840 (which is the NI Manufacturer ID, RobotController type, Device ID 0 and API ID 0x061). It is an 8 byte CAN packet with the following bitfield layout.

Description	Byte	Width (bits)
Match time (seconds)	8	8
Match number	6-7	10
Replay number	6	6
Red alliance	5	1
Enabled	5	1
Autonomous mode	5	1
Test mode	5	1
System watchdog	5	1
Tournament type	5	3
Time of day (year)	4	6
Time of day (month)	3-4	4
Time of day (day)	3	5
Time of day (seconds)	2-3	6
Time of day (minutes)	1-2	6
Time of day (hours)	1	5

struct [[gnu::packed]] RobotState {
  uint64_t matchTimeSeconds : 8;
  uint64_t matchNumber : 10;
  uint64_t replayNumber : 6;
  uint64_t redAlliance : 1;
  uint64_t enabled : 1;
  uint64_t autonomous : 1;
  uint64_t testMode : 1;
  uint64_t systemWatchdog : 1;
  uint64_t tournamentType : 3;
  uint64_t timeOfDay_yr : 6;
  uint64_t timeOfDay_month : 4;
  uint64_t timeOfDay_day : 5;
  uint64_t timeOfDay_sec : 6;
  uint64_t timeOfDay_min : 6;
  uint64_t timeOfDay_hr : 5;
};

If the System watchdog flag is set, motor controllers are enabled. If 100 ms has passed since this packet was received, the robot program can be considered hung, and devices should act as if the robot has been disabled.

Note that all fields except Enabled, Autonomous mode, Test mode, and System watchdog will contain invalid values until an arbitrary time after the Driver Station connects.