Installation Guide

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 For safety-critical CAN bus (e.g. so-called “hot bus”) installations where a hard disconnect must be

guaranteed and physical safety is needed, the 120 Ω termination jumper must be removed. This will

guarantee that termination resistors cannot be accidentally enabled by software, potentially disrupting

the CAN bus. Note that permission from the customer to connect to a safety critical CAN bus should

always be obtained.

 If the installer is in doubt as to the safety critical nature of the CAN bus, the jumper must be left off.

 After installation of the MiX 4000 and configuration of the termination resistance the CAN bus should

measure as 60 Ω, with the unit powered on and if not, the settings should be checked.

 Note that the MiX 4000 terminating resistor automatically disconnects from the CAN bus if the MiX 4000

unit loses power.

13.1.6 When must the RD/WR Jumpers be in the circuit?

 For non-safety-critical CAN bus installations, it is recommended to leave the transmit enable jumper fitted

and configure the transmit enable to OFF or ON in software, as needed, as this allows the maximum

flexibility.

 For OBDII connections the RD/WR (transmit enable jumper) must be fitted, since OBDII is a

request/response protocol and requires the MiX 4000 to transmit messages on the CAN bus.

 For safety-critical CAN bus (e.g. so-called “hot bus”) installations where guaranteed, physical safety is

needed, the transmit enable jumper must be removed. This will guarantee that transmissions cannot be

accidentally enabled by software, potentially disrupting the CAN bus.

 Note that permission from the customer to connect to a safety critical CAN bus should always

be obtained.

 If the installer is in doubt as to the safety critical nature of the CAN bus, the jumper must be left off.

 Some FMS gateways requires an acknowledgement ("ACK") on the physical layer and the RD/WR

(transmit enable jumper) must be fitted for the CAN chip to be able to assert the "ACK" bit in the header,

otherwise the host will stop transmitting any CAN messages. See diagram below. Note that no messages

are transmitted on the CAN bus, the messages are just acknowledging, so this is a safe mode.