Moving from IEEE488/RS232 connectors to Ethernet.By Thomas Mullineaux, Ophir RF Inc.
Look on the rear panel of most test instruments and you will see IEEE488/RS232 connectors. These interfaces have dominated test system control interconnection for many years, and with good reason. For instance, regarding the IEEE488, many electrical engineers have grown up with this connection method, it has a well defined protocol, and is well suited to applications where the environment is benign, and there is no need for great speed or distance. Since this description suits most ATE test environments, IEEE488 remote control and monitoring has reigned supreme for many years, and due to its 'industry standard' grip, is sure to reign for many years to come.
However, all products have a finite lifespan, and few can resist the encroachment of emerging and steadily improving technologies. The contender eminently placed to bring about the end of the dominance of industry standards such as the IEEE488, is PC LAN connection technology.
The use of Ethernet connection using TCP/IP (Transmission Control Protocol/ Internet Protocol) has exploded due to the growth of the Internet. The same technology has been used to form Local Area Networks (LANs) with the result that Ethernet LAN interface cards are readily available and inexpensive. This, together with a steadily increasing pool of Ethernet savvy staff could be the beginning of the end of the dominance of IEEE488.
Qualitative Description of
An Ethernet LAN interface card and a PC running a regular web browser are all that are required to interface with a piece of test equipment. In the description below, the test equipment is a RF power amplifier. The controlling computer can be running MS Windows, Apple OS, Linux or Unix, etc.
Detailed RF Power Amplifier
Ethernet Interface Description
Figure 1 shows the amplifier connected to a standard LAN using Category -5 10-Base T port wiring (RJ45 connector). This connection permits local connection via a LAN or indeed, worldwide connection via the Internet.
The card inside the amplifier incorporates a special-purpose Web page server, providing detailed information on the amplifier's status in HTML (HyperText Markup Language). The card also supports DHCP (Dynamic Host Configuration Protocol) to allow seamless integration with existing networks. If required, the IP address of the card may be set via a separate port on the card.
The screenshot (Figure 2) shows the 'form' permitting control and monitoring of the amplifier via the Ethernet interface. Data inputs to set the amplifier parameters are made by clicking in the relevant text entry box and entering the data via the PC keyboard. Radio buttons are used to change the status of the amplifier and to submit data that has been entered into the relevant box. The read back data on the screen is refreshed at regular periods determined by the user.
Radio buttons/Data Input boxes permit:
Control of the amplifier RF Output Mode (Amplifier ON or in STANDBY)
Control of the amplifier gain. This is achieved by setting the level of the amplifier's internal VVA (Voltage controlled Variable Attenuator)
Control of the reflected power alarm threshold
Monitoring of the forward RF power value
Monitoring of the reflected RF power value
Monitoring of the amplifier fault status, i.e., excess reflected power
No special hardware or software is required for this interconnection and distance is not a constraint as the amplifier can be controlled from the other side of the world. However, to replicate IEEE488, further instruments must be connected to form a multiplexed 'talker/listener' loop. Also, the RF power amplifier will continue to be provided with IEEE488/RS232 connectors along with the Ethernet connector for the foreseeable future.