1. Device purpose

This device is a CAN/CAN FD interface based on:

Nucleo-G474RE
CAN-FD HAT by Embedded Garage

The firmware provides three active protocol modes over USART2:

CLI, a text service console
SLCAN, an interface compatible with Lawicel/SLCAN class applications
GVRET, a binary protocol compatible with SavvyCAN GVRET interface class tools

The firmware supports three FDCAN controllers:

CAN1
CAN2
CAN3

2. Startup behavior

After a successful start, the application initializes Flash, licenses, system LEDs, inputs, UART, CAN, router, and trigger modules.
The default active protocol after boot is CLI.
All three CAN buses are initialized during startup.
Default rates are 100000 bps for the nominal phase and 1000000 bps for the CAN FD data phase.

Note:

CAN configuration (speeds, enable/disable, listen-only, filters), routing (forwarding), relay triggers, and input triggers are saved automatically to Flash on every change, provided the Store Config license is active.
Without the Store Config license, configuration changes apply at runtime but are not retained after reboot.
License data is written with the lic command and does not require the Store Config license.
The active protocol (CLI/SLCAN/GVRET) is saved to Flash on every change.

3. Host interface

Communication with the host uses USART2.

Baudrate depends on the active protocol:

CLI: 115200 bps
SLCAN: 115200 bps
GVRET: 1000000 bps

Other UART settings:

8 data bits
no parity
1 stop bit
no flow control

The UART layer uses DMA and buffering:

DMA RX: 256 bytes
RX buffer: 2048 bytes
TX buffer: 2048 bytes
CLI command buffer: 256 characters
SLCAN command buffer: 64 characters

4. Hardware elements

4.1 12V inputs

Four digital 12V inputs are available:

The inputs are active high and use 50 ms software debounce.

4.2 Buttons

Six buttons are available:

Buttons are active low and use 50 ms debounce.

In the current application version, only this one is used directly:

SW1: switch active protocol

SW3-SW6 can be used by the inp_trig function as button trigger sources.

4.3 Relay outputs

Four relay outputs are available:

In the current firmware version, Q1-Q4 do not indicate CLI/SLCAN/GVRET mode. They are intended for relay trigger functionality if configured by a CLI command and enabled by the corresponding license.

4.4 System LEDs

The board has system LEDs:

RDY
BUSY

RDY LED meaning:

startup: 1000 ms ON / 200 ms OFF pattern
normal operation: steady ON
warning: 500 ms ON / 500 ms OFF
critical error: 100 ms ON / 100 ms OFF

BUSY LED meaning:

driven by a pattern corresponding to the current protocol. According to the number of pulses:
- 1: CLI control (console)
- 2: SLCAN/LAWICEL protocol
- 3: GVRET protocol

Additionally, each CAN bus has separate RX and TX LEDs driven by frame activity.

5. CAN buses

Firmware supports:

Classic CAN
CAN FD
CAN FD with BRS
standard 11-bit and extended 29-bit identifiers
DATA and RTR frames

Default startup rates for CAN1, CAN2 and CAN3:

nominal bitrate: 100000 bps
CAN FD data bitrate: 1000000 bps

Available nominal bitrates:

1000
2000
5000
10000
20000
50000
100000
125000
250000
500000
1000000

Available CAN FD data bitrates:

1000000
2000000
4000000
5000000
8000000

CAN buffers and queues:

RX queue: 16 frames per interface
TX queue: 16 frames per interface
standard filters: 28 entries
extended filters: 8 entries

By default, frame forwarding to the console is enabled for CAN1 only. Forwarding from the active protocol to CAN1 is enabled by default. CAN-to-CAN forwarding is disabled by default.

6. Operating modes

6.1 CLI

CLI is active after startup. The user communicates through a serial terminal and enters text commands terminated with Enter.

Commands available in CLI:

help [command] – list commands or details for a selected command
can_tx <bus> <id_hex> <S|E> <D|R> <C|F|B> <len> [data_hex] – send a CAN or CAN FD frame
can_status – forwarding matrix table (source vs target)
can_en <bus> <E|D> – enable or disable a bus
can_silent <bus> <E|D> – enable or disable listen-only
can_fwd_set <source_bus> <target_bus> <0|1> – CAN-to-CAN, CAN-to-active-protocol, or protocol-to-CAN routing; 0 in bus field means protocol; source_bus = 0 and target_bus = 0 simultaneously is not allowed
can_speed <bus> <bitrate> – set nominal bitrate
can_fd_speed <bus> <bitrate> – set CAN FD data phase bitrate
can_filter <bus> <idx> <M|R|D> <id1_hex> <id2_hex> <S|E> <R|N|A> – configure CAN filter
can_filters_get <bus> – read filter list
rly_trig <relay> <bus> <S|C|T|P> <id_hex> <S|E> <len> <D|R> <C|F|B> <mask_hex> <value_hex> [duration_ms] – configure relay control based on CAN frame
rly_trig_get <relay> – read relay trigger configuration
inp_trig <input> <R|F|H> <interval_ms> <bus> <id_hex> <S|E> <D|R> <C|F|B> <len> [data_hex] – send CAN frame on input event
inp_trig_dis <input> [R|F|H] – disable input trigger
inp_trig_get – read input trigger configuration
lic <idx> <hash64> – write license hash to Flash
lic_get – device UID, license slot contents, and active feature status
default_config – restore default configuration in Flash memory
reboot – reboot the device

Abbreviations in CLI:

S and E mean standard or extended identifier
D and R mean DATA or RTR
C, F, B mean Classic CAN, CAN FD, and CAN FD with BRS
in can_filter: M = mask, R = range, D = dual, and actions are R = reject, N = none, A = accept
in rly_trig: S = set, C = clear, T = toggle, P = pulse
in inp_trig: R = rising, F = falling, H = hold

CLI command examples:

help
help can_tx
can_tx 1 1F0 S D C 8 1122334455667788
can_tx 3 123 S D B 12 00112233445566778899AABB
can_speed 1 500000
can_fd_speed 1 2000000
can_en 2 D
can_silent 2 E
can_fwd_set 1 2 1
can_fwd_set 2 0 1
can_fwd_set 0 1 1
can_filter 1 0 M 123 7FF S A
lic_get

CLI limitations in current code:

can_filter requires an active Extended CAN filters license
rly_trig* functions require an active CAN relay trigger license
inp_trig* functions require an active CAN button trigger license
writing configuration to Flash on every change requires an active Store Config license

6.2 SLCAN

SLCAN is the second active router protocol. Protocol is switched with SW1.

SLCAN is connected only to:

CAN1

Supported SLCAN parser commands:

O – open CAN1
C – close CAN1
Sx – set nominal bitrate for CAN1
Yx – set CAN FD data phase bitrate for CAN1
V – get firmware version string (Vxx.yy)
t, T – transmit classic DATA frames
r, R – transmit classic RTR frames
d, D – transmit CAN FD without BRS
b, B – transmit CAN FD with BRS

SLCAN bitrate mapping:

S0 = 10000
S1 = 20000
S2 = 50000
S3 = 100000
S4 = 125000
S5 = 250000
S6 = 500000
S8 = 1000000

SLCAN CAN FD data bitrate mapping:

Y1 = 1000000
Y2 = 2000000
Y4 = 4000000
Y5 = 5000000
Y8 = 8000000

Example SLCAN frames and commands:

O – open CAN1 for operation in SLCAN mode
C – close CAN1
S6 – set CAN1 nominal speed to 500000 bps
Y2 – set CAN FD data phase speed to 2000000 bps
t12381122334455667788 – standard Classic CAN DATA frame with ID 0x123, length 8 bytes, and data 11 22 33 44 55 66 77 88
T1ABCDEFF411223344 – extended Classic CAN DATA frame with ID 0x1ABCDEFF, length 4 bytes, and data 11 22 33 44
r3210 – standard RTR frame with ID 0x321 and length 0
R1ABCDEFF8 – extended RTR frame with ID 0x1ABCDEFF and length 8
d123CAA55AA55AA55AA55AA55 – standard CAN FD frame without BRS, ID 0x123, DLC C meaning 24 data bytes; after DLC, 48 hex characters are required
D1ABCDEFF9AABBCCDDEEFF001122334455 – extended CAN FD frame without BRS, ID 0x1ABCDEFF, DLC 9 meaning 12 data bytes
b1239AABBCCDDEEFF001122334455 – standard CAN FD frame with BRS, ID 0x123, DLC 9 meaning 12 data bytes
B1ABCDEFFA00112233445566778899AABBCCDDEEFF – extended CAN FD frame with BRS, ID 0x1ABCDEFF, DLC A meaning 16 data bytes

Transmit frame format description:

t and r mean standard 11-bit ID
T and R mean extended 29-bit ID
d and D mean CAN FD without BRS
b and B mean CAN FD with BRS
after ID there is a single DLC character in hex format
for Classic CAN frames, DLC 0-8 equals the number of data bytes
for FD frames, parser DLC mapping follows CAN FD standard: 9=12, A=16, B=20, C=24, D=32, E=48, F=64 bytes
RTR frames do not include a data field after DLC
all commands must end with CR or LF

SLCAN limitations in this version:

only CAN1 is handled by the SLCAN parser (protocol limitation)
only non-FD frames up to 8 bytes are reported to the host
commands F, M, m, N, s are recognized by the parser but do not provide full end-user functionality
outgoing host frames include a timestamp in ms sent modulo 0xFFFF

6.3 GVRET

GVRET is the third active router protocol. Protocol is switched with SW1.

GVRET uses binary frames with SOF byte 0xF1.

Supported GVRET commands handled by the parser:

0x00 – CAN frame from host to device
0x05 – set CAN1/CAN2 configuration (enable, listen-only, nominal bitrate)
0x06 – get CAN1/CAN2 status
0x07 – get device info (includes firmware version)
0x09 – communication validation
0x0C – get bus count
0x0D – get extended bus info (CAN3)
0x0E – set extended bus config (CAN3)
0x01 – time synchronization

GVRET behavior in current firmware:

reported bus count is 3 (CAN1, CAN2, CAN3)
incoming CAN traffic is reported to GVRET for all three CAN buses
both Classic CAN and CAN FD frames are sent to the host
host-to-device transmit parser currently handles 0x00 CAN frame command; 0x14 CAN FD host transmit is not handled

7. Licenses

The license system uses the MCU UID and stores 32-byte SHA-256 hashes in user Flash.

Licensed features:

Extended CAN filters
CAN relay trigger
CAN button trigger
Store config (automatic saving of configuration to non-volatile memory on every change)

8. Trigger features

8.1 Relay trigger

Each Q1-Q4 relay can react to a matching CAN frame.

Available modes:

ON/OFF
TOGGLE
PULSE with duration in milliseconds

Matching includes:

bus number
CAN identifier
standard or extended ID type
RTR or DATA
Classic CAN or CAN FD
BRS
data length
data mask and value

8.2 Input trigger

Inputs and buttons can send a configured CAN frame on event:

rising (button press / applying 12V signal)
falling (button release / signal release)
hold with periodic interval – sent while the button is held or while 12V is present on one of the Ix inputs

Input mapping for inp_trig command:

I1 to I4
B3 to B6 for SW3-SW6 buttons

Input mapping for inp_trig_dis command:

I1 to I4
B3 to B6 for SW3-SW6 buttons

9. Quick start

Connect Nucleo-G474RE and CAN-FD HAT.
Drag the .hex file to the virtual USB drive.
Open terminal at 115200 8N1.
After startup, run help.
Check interface status with can_status.
If needed, set speeds using can_speed and can_fd_speed.
Send a test frame with can_tx.
To switch to SLCAN, press SW1 and use Lawicel-compatible commands on CAN1.
To switch to GVRET, press SW1 again and connect host software at 1000000 bps (8N1), for example SavvyCAN in GVRET mode.

10. Diagnostics

No UART communication:
- check active protocol and required baudrate (CLI/SLCAN: 115200, GVRET: 1000000)
- check USART2 connection
- check whether host sends CR or LF line endings
No CAN frames:
- check 120 Ohm termination
- check bitrate match on both bus sides
- check can_status
- check whether bus is in can_silent mode
- check whether interface was disabled with can_en <bus> D
No relay trigger or input trigger reaction:
- check lic_get
- confirm required license is active
- check ID, frame type, length, and masked data match
Incomplete SLCAN support:
- expected in this version due to CAN1-only support and missing full implementation of F, M, m, N, s

User Manual – EG CAN Firmware v1.3