Reference — J1939 gateway

The MUXEN devices this gateway publishes

Device	Function	Instance	What it carries
Generator group	4	the genset's own J1939 instance, then InstanceNum	one per discovered genset: state, engine speed, AC voltage, current, power, temperature, alarms
Generic I/O	17	configured (InstanceNum)	the box's own relays, inputs and analog inputs

MQTT topics on the Brain follow device/<function>/<instance>/<frame>:

Topic	Direction	Contents
device/4/<n>/life	published, 1 s	state, stateCode, voltage, temperature, noStart, noCutOff
device/4/<n>/state	published, 1 s	rpm, voltage, current, power
device/4/<n>/error/<code>	published, 500 ms	one topic per active alarm
device/4/<n>/command	accepted	startRequest, stopRequest, ForceCmd, clearError
device/17/<n>/life	published	the box's own inputs and relays

Genset states: off, contact, starting, on, stopping, error, plus codes 5 (engine only) and 6 (test mode), which carry no label.

Parameters — generator group (function 4)

Parameter	Default	Meaning
InstanceNum	the genset's J1939 instance	the MUXEN instance; changing it needs a restart
BindToParc	latched to 255 (stand-alone) at first sight	the battery zone this genset charges. Required for automatic start; read once at discovery
SocToStart	15	state of charge, in %, below which the genset is started
MaxCurrentPercent	40	share, in %, of the zone's maximum discharge current above which the genset is started to assist
SocToStopAfterCurrentHelp	90	state of charge, in %, above which an assist run may end
ChargeCurrentToStop	−100	battery current, in 0.1 A, at which a full bank counts as charged
GensetModel	set by discovery	read-only: 1 = Fischer Panda, 2 = Cummins Onan
MinSocToStop, VmaxToWork	5, 248	in the list, not used by this firmware
ProductId, HardwareId, SoftwareId, SoftwareVersion	read-only	see Reference

Every threshold above concerns a Fischer Panda only.

Parameters — generic I/O (function 17)

The common ones (InstanceNum, EnGenIo, EnAnalogPwr) are in Reference. This firmware adds four:

Parameter	Default	Meaning
Relay1Eqn, Relay2Eqn	empty	a MUXEN equation driving that relay from what it hears on the bus
Relay1Latch, Relay2Latch	0	1 = each time the equation goes true, the relay toggles instead of following it

A relay command from the bus overrides the equation until released.

Routines

Routine	Payload	Effect
1	0001	restore the instance number to its default
1	any bit above bit 0	restore every other parameter of that device
2	—	reserved; does nothing, including no LED "locate"

What is read from the J1939 bus

Fischer Panda — manufacturer-specific frames:

PGN	Feeds
65281	genset state, and the genset's own auto-start mode
65300	AC voltage, current, power
65303	engine speed
65285	engine temperature

Cummins Onan:

PGN	Feeds
65280	genset status → the MUXEN state
61444	engine speed
65030	AC line-to-neutral RMS voltage
65262	temperature
65226, 65227	active and previously active diagnostic codes → MUXEN alarms
65242, 65253, 65263, 65266, 65270, 65271	accepted and decoded, but nothing is published from them today

Everything else is ignored; an unknown sender is asked once to introduce itself so the gateway can decide whether it knows it.

What is written to the J1939 bus

Only for a Fischer Panda:

Frame	Purpose
PGN 61184	remote start and stop; and re-enabling the genset's auto-start mode whenever it is found off
PGN 65305	charge parameters taken from the bound battery zone: state of charge, maximum charge voltage, maximum charge current

The gateway claims source address 0x53 (83) for itself and answers address-claim requests.

Timings

Genset life and state frames	every 1 s, starting 1 s after discovery
Alarms republished	every 500 ms
A Fischer Panda is forgotten after	120 s without a single J1939 frame from it
A Cummins Onan is reported off after	5 s without a single J1939 frame from it (CUMMINS_ONAN_ASLEEP_TIMEOUT_MS); it is never forgotten
Generic I/O published	on change, and at least every 500 ms
Second CAN bus bitrate	250 kbit/s, forced at every start

Known limitations

• A diagnostic code the gateway does not recognise clears the whole alarm list, including alarms belonging to other devices.
• The temperature published for a Cummins Onan is derived from its fuel temperature and its offset is wrong. Indicative only.
• Charge parameters are sent to J1939 address 0 rather than to the genset's own address; a Fischer Panda that does not sit at address 0 never receives them.
• clearError is accepted and ignored.
• Current and power are never published for a Cummins Onan.
• InstanceNum and BindToParc take effect only after a restart.

Versions

Hardware	Version	Image
CanCan v1	5.3	010010034-app_j1939-firmware.srec
CanCan v2	6.4	010010034-V2-app_j1939-firmware.srec

Source: workspace/muxen/cancan/app_j1939/, overlay boards/arm/<board>/010010034.overlay.