ToolLink User Manual
MKS Instruments, Inc.
Page 10 of 30
Chapter 3 – Theory of Operation
This chapter describes how the CDN46X gateway operates. You should have a working knowledge of
DeviceNet and asynchronous serial communications before continuing. The Open DeviceNet Vendors
Association (
www.odva.com
) is a good source for general DeviceNet information. Refer to your serial
device documentation for its protocol information.
DeviceNet Interface
The DeviceNet Specification defines an Object Model that consists of Objects and Attributes. An Object
is a predefined software process, and an Object Attribute is a data value used or created by that process.
An Object can have multiple Instances, or the same process operating with different sets of Attributes or
data values. For the purpose of this document, an Object Instance is an independent program or
process, and its Attributes are configuration parameters and data values that are unique to that specific
Object Instance.
The CDN46X gateway has six different Object Classes, or types. Five are standard objects defined by
the DeviceNet Specification (
Identity, Router, DeviceNet, Assembly, Connection
). One specific object
defines for the CDN46X gateway (
Serial Stream)
. The
Serial Stream Object
configures the serial channel,
and scans the incoming serial stream for valid message packets
The CDN46X gateway operates as a DeviceNet slave. It supports Explicit Messages and Polled I/O
Messages of the predefined master/slave connection set. The Explicit Unconnected Message Manager
(UCMM) is not supported. The CDN466 will be a Group 2 Only Slave device. It will support Change-of-
State and Polled I/O Messages. It will also support Explicit Messaging. The DeviceNet interface will
comply with the DeviceNet Physical Layer specification.
The I/O Messaging process consists of the DeviceNet master sending output data to the CDN46X in the
form of a Poll/COS Command Message, and the CDN46X returning input data to the DeviceNet master in
a Poll/COS Response Message. The difference between Poll and Change-of-State is Polled I/O
Messaging is initiated by the DeviceNet master and responded to by the slave device
The output and input data bytes are typically mapped into data files inside the DeviceNet master. These
data files are exchanged with the user application program, which acts upon the received input data and
writes new output data to the DeviceNet master.
CDN46X
Gateway
DeviceNet
Master
Application
Program
Input File
Output File
Serial
Device
DeviceNet network
Outputs
Inputs
Receive
Message Packet
Transmit
Message Packet
DeviceNet I/O Command
output data
DeviceNet I/O Response
input data
