Vansco VMM3120, User Manual

Page: 54 / 92

44 VMM3120
Communication
The following table provides specifications for the CAN:
CAN Specifications
Item MIN NOM MAX UNIT
Baud rate limitations (hardware) - - 1000 kbps
Baud rate limitations (software) - 250 - kbps
Wake on CAN current draw - - 500 uA
Termination resistor 120 - -
Ω
6.1.2. J1939 CAN Configuration
There are two features associated to CAN communication that are configured:

Wake on CAN - the VMM3120 will turn on when a CAN message is
received.

Internal CAN Termination Resistor - the VMM3120 does not have a 120 Ω
CAN termination resistor embedded inside the module, which is required to
use CAN communication. You are required to design it into the vehicle
harness.
Note: Putting CAN termination resistors in the module would violate the
J1939 specification, which states that the resistor should be designed into the
harness.
6.1.3. J1939 CAN Installation Connections
The CAN connection for the VMM3120 should conform to the J1939 standard.
The J1939 standard is a robust automotive specification that is a good CAN
installation guideline even when the J1939 CAN protocol is not being used.
For a list of J1939 connection considerations, refer to the SAE J1939
specifications available through the Society for Automotive Engineers. SAE
J1939-11 covers the physical aspects of the CAN bus including cable type,
connector type, and cable lengths.
Note: The standard variant of the VMM3120 does not have a CAN
termination resistor, which is based on the assumption that the CAN bus is
terminated in the harness.
The following lists the elements that are required for a J1939 CAN connection:

CAN Cable: A shielded twisted-pair cable should be used when connecting
multiple modules to the CAN bus. The cable for the J1939 CAN bus has three
wires: CAN High, CAN Low, and CAN Shield (which connect to the
corresponding CAN_HIGH, CAN_LOW, and CAN_SHIELD pins on the
connector). When a module does not have a CAN_SHIELD pin, the CAN