GMW3089 5th Edition, January 1, 2015
General Motors Local Area Network (GMLAN) Single Wire Controller Area
Network (SWCAN) Physical and Data Link Layers Specification
This document specifies the physical layer requirements for a
Carrier Sense Multiple Access/Collision Resolution (CSMA/CR) data
link which operates on a single wire medium to communicate among
Electronic Control Units (ECU) on road vehicles at normal
transmission rates of 33.333 kbits/s and at a special high speed
assembly or service transmission bit rate of 83.333 kbits/s.
This document is to be referenced by the particular Component
Technical Specification (CTS) which describes any given ECU in
which the single wire data link controller and physical layer
interface is located. Only the performance of the data link
physical layer is specified in this document. ECU environmental and
other requirements shall be provided in the ECU CTS. The intended
audience includes, but is not limited to ECU suppliers, Controller
Area Network (CAN) controller suppliers, CAN transceiver suppliers,
component release engineers and platform system engineers.
Applicability. This specification describes the
physical layer requirements for a single wire data link capable of
operating with various CSMA/CR protocols such as the CAN version
2.0. This serial data link network is intended for use in
applications where high data rate is not required and a lower data
rate can achieve cost reductions in both the physical media
components and in the microprocessor (μP) and/or dedicated logic
devices which use the network.
The network shall be able to operate in either the normal data
rate mode or a high speed data download mode for assembly line and
service data transfer operations. The high speed mode is only
intended to be operational when the bus is attached to an off-board
service node. This node shall provide temporary bus electrical
loads which facilitate higher speed operation. Such temporary loads
shall be removed when not performing download operations.
This physical layer specification includes such transceiver
requirements as are necessary to ensure that the bus voltage
signals and that a common Integrated Circuit (IC) footprint can be
achieved across all applications. The transceiver requirements are
specified in Appendix A.