GE HE500TIU112 manual Networks, Scope Controller Area Network can Overview, CsCAN Network Overview

CH. 8: NETWORKS	06 Apr 2000	PAGE 37
		GFK-1819

CHAPTER 8 : NETWORKS

8.1Scope

This chapter gives a brief introduction into the networking hardware available on the Operator Station range. The part numbers of the various options are available in the Introduction Chapter of this manual. For information on programming the various network options see GFK-1818, User Manual for the CBREEZE Software.

8.2Controller Area Network (CAN) Overview

The controller area network (or CAN bus) is a serial communications bus that was originally developed in the late 1980’s by a German company (Robert Bosch) for use in the automotive industry. CAN is an ISO (International Standards Organisation) - defined serial communications bus for real-time applications.

Established in 1947, the International Standards Organisation (ISO) is a multinational body dedicated to worldwide agreement on international standards. Specifically, CAN is documented in ISO 11898 (for high-speed applications) and ISO 11519 (for lower-speed applications).

8.2.1CAN Features

CAN-based open automation technology successfully competes on the market of distributed automation systems because of the special features of the CAN protocol. The special features are CAN’s producer- consumer-oriented (or peer-to-peer) principle of data transmission and its multi-master capability. The general design of CAN originally specified a high bit rate, high immunity to electrical interference and an ability to detect any errors produced. CAN networks have the following general attributes:

•Automatic error detection

•Easily configurable

•Cost-effective to design and implement

•Capable of operating in harsh environments

8.3CsCAN Network Overview

The CsCAN Network was first developed in 1993 by Horner Electric. It was developed for use in a project that Horner Electric completed for the United States Post Office. Horner Electric developed its own network, because it needed a network that had a specific set of powerful peer-to-peer and host-to-node capabilities. The CsCAN Network has a “pass-through” feature whereby PC-based programs access other nodes connected to a network by passing the programming command through the serial port to the network port. (For a more detailed description, see below.) Horner Electric found that by developing its own network, it satisfied several important needs. Horner Electric continues CsCAN Network development to satisfy the requirements of today and the requirements of the future.

8.3.1CsCAN Network Features

The CsCAN Network is based on CAN, which has many desirable features such as ruggedness, ease of configuration, etc. With Horner Electric Controllers, data is passed at 125Kbps using a differential pair of wires plus a ground. It is important to note that the data rate is not limited to 125Kbps. The maximum data rate is 1Mbps (limited by the speed of light). The CAN implementation in the CsCAN controller allows up to 64 controllers to be networked with no additional hardware and up to 253 controllers with three CAN repeaters.

For the programmer, little knowledge of networking procedures is needed. However for troubleshooting and optimizing, the following information is helpful. Instead of using master/slave or token passing, the hardware self-arbitrates based on the Network ID. Controllers with lower Network ID numbers are given a higher priority than controllers with higher Network ID numbers.

8.3.2CsCAN Network Operation

When a controller needs to send data over the network, it first waits for the network to be idle (currently a maximum of 900uS). If two controllers start broadcasting information on the network at the same time, the