The CAN protocol

Overview

The CAN messages are identified by identifier. Loco-CAN uses its own ID-system. Every module can send messages and register to ids that are interesting. There are some spezial messages, that have a spezial impact on the overall function. Primary it is the communication between controllers and the motor module.

Loco-CAN uses the extended 29 bit identifiers. The 11 bit standard id contains the message type, 16 bits of the extended id holds an unique hardware id of the module. This uuid is used for the setup of module parameters.

Heartbeat

Heartbeat messages are used to identify the presents of modules. There are different heartbeats:

Module heartbeat: Each module sends an identification message contain
Controller heartbeat
Heartbeat and the Controller priority

There are no limitations of controllers connected to the bus, but only one can be active. When the main switch of a controller is set to on, it checks, if another controller is sending a heartbeat. In this case an error is displayed and the controller stays inactive. To ensure a safe operation some functions can be configured to react on a heartbeat message. The heartbeat is sent from the active controller. In the system only one controller can be activated for a locomotive. A missing heartbeat leads to an emergency stop.

Status Messages

A status message is sent by each locomotive.

Operation Messages

High priority messages

Name	Value
CAN_ID_CURRENT	0x100
CAN_ID_MOTOR_CURRENT	0x110
CAN_ID_BATT_CURRENT	0x120
CAN_ID_LIGHT_CURRENT	0x130

Mid priority messages

Name	Value
CAN_ID_SPEED	0x200
CAN_ID_DIR	0x210
CAN_ID_SIGNAL	0x220
CAN_ID_TACHO	0x230

Low priority messages

Name	Value
CAN_ID_VOLTAGE	0x300
CAN_ID_MOTOR_VOLTAGE	0x310
CAN_ID_BATT_VOLTAGE	0x320
CAN_ID_BATT_1_VOLTAGE	0x321
CAN_ID_BATT_2_VOLTAGE	0x322

Command messages

Name	Value
CAN_ID_DRIVE	0x400
CAN_ID_LIGHT	0x410
CAN_ID_SWITCH	0x420

Status messages

Name	Value
CAN_ID_STATUS	0x500

Heardbeat values

The drive heartbeat is sent from the active controller and used to monitor the connection between controller and motor modules. The train end latern signals are registered in the controller when starting to drive. A change in the latern signal list while driving leads to a emergency stop (switch off the heartbeat signal)

Name	Value
CAN_ID_DRIVE_HEARTBEAT	0x010
CAN_ID_TRAINEND_HEARTBEAT	0x020

sent from train end laterns

Setup

The setup command is used to send and receive module setup data.

0x7FF request setup info from module (0 byte message length) the identifier uuid is ignored and the info is sent any way
0x7nn returns info packages (nn = data id) + 8 bytes text description adding the own uuid in the extended identifier so no other module can interpret it as a write command
write commands are sent with the target uuid in the first two bytes 0x600 set module name

0x6nn set data nn => data id + max 8 bytes of data

message bytes 0, 1 => UUID of module byte 2 => message id
0xFF = module name bytes 3-7 => data

Masks

Name	Value
CAN_ID_MASK	0x770
CAN_REQUEST_MASK	0x7FF
CAN_ID_REQUEST	0x7FF
CAN_REPLY_MASK	0x7FF
CAN_ID_REPLY	0x780
CAN_SETUP_MASK	0x700
CAN_ID_SETUP	0x700

Name	Value
CAN_NAME_MAX_SIZE	5
CAN_VALUE_MAX_SIZE	6