Low Speed GMLAN Circuit Description

The data link connector (DLC) allows a scan tool to communicate with the low speed GMLAN serial data circuit. The serial data is transmitted over a single wire to the appropriate control modules. The transmission speed for low speed GMLAN is up to 83.33 Kb/s. Under normal vehicle operating conditions, the speed of the bus is 33.33 Kb/s. This protocol produces a simple pulse train sent out over the low speed GMLAN serial data bus. When a module pulls the bus high, 5 volts, this creates a dominant logic state or 0 on the bus. When the bus is pulled low, 0 volts, it is translated as a recessive logic state or 1. To wake the control modules connected to the low speed GMLAN serial data bus, a high voltage wake up pulse is sent out over the bus, the voltage level of the pulse is +10 volts. Modules connected to the low speed GMLAN bus can be part of a virtual network as described in the previous paragraph. The modules on the low speed GMLAN serial data bus are connected to the bus in a parallel configuration.