GE LM10 A.1.4 Explicit Messaging and Input/Output I/O Messaging, A.1.6 DeviceNet Features

CHAPTER A: DEVICENET OVERVIEW

A.1.4 Explicit Messaging and Input/Output (I/O) Messaging

Explicit messages contain information such as vendors, parameters, etc. of a device. This information is comparatively less important than the I/O message; as such, it is sent with a higher CAN identifier as not to disturb the exchange of I/O messages on the bus.

Input/Output (I/O) messages contain the real-time I/O information of a device. In order to achieve “real time”, these messages are sent as quick as possible; therefore, they are sent with a lower CAN identifier than explicit messages.

A.1.5 Pre-defined Master/Slave Connection Set

A set of connection identifiers known as the Pre-defined Master/Slave Connection Set has been specified to simplify the movement of I/O configuration-type data typically seen in a master/slave architecture. An important benefit is that the establishment of connections from the pre-defined set is simplified considerably. Only a few messages are required to have I/O connections up and running. The pre-defined set contains one explicit messaging connection and allows several different I/O connections including:

•bit strobed command/response

•polled command/response

•change of state

•cyclic

A.1.6 DeviceNet Features

DeviceNet's features include:

1.Low cost.

2.High speed. DeviceNet supports 3 baud rates: 125 kbps, 250 kbps, and 500 kbps. This meets 95% of typical industrial requirements.

3.Reliability. DeviceNet uses the well proven CAN protocol with application layers that have undergone strict conformance testing to ensure reliability.

4.Support of up to 64 active nodes.

5.Easy installation.

6.Removal and replacement of devices from the network under power.

7.0 to 8 byte data packets.

8.Linear (trunk line/drop line) bus topology, with power and signal on the same network cable.

A.1.7 Maximum Cable Lengths for DeviceNet

DeviceNet defines the maximum cable lengths (trunk and drop cables) to ensure the propagation of the transmitted message falls within the acceptable limits. The upper boundaries of the trunk cable and drop cable length are shown below.

LM10 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL A–3