Global Sources
EE Times-Asia
Stay in touch with EE Times Asia
EE Times-Asia > Embedded

Less-than-$100 module puts TTL I/O on your network

Posted: 10 Jun 2005 ?? ?Print Version ?Bookmark and Share

Keywords:saelig? etherI/o24 module? etherI/o24? ethernet network?

Once again Saelig Co. comes up with a simple, but unique, niche product that can make life easierand perhaps inject a bit of fun into your system, too (use it to remotely flip that coffee pot on down in the lab).

The CSMA/CD architecture of non-switched Ethernet networks (with inherent collisions, packet loss, and probabilistic transfer timing) is an obstacle to deterministic Ethernet communications. It's a new ballgame with switched Ethernet and full-DUX communications, though, and that's where this module comes in.

When installed on any 10Base-T Ethernet network, the intelligent EtherI/O24 module therefore comprises a deterministic I/O platform.

Latency from command receipt to response transmission of less than 500?s under all circumstances (if short I/O packets are used, latency will be less than 200?s). The speed of the Ethernet interface to the control system lets over 1-million inputs per second be read. Likewise, a million outputs per second can be controlledusing off-the-shelf Ethernet switches.

Software versatility

One thing not mentioned in Saelig's release notes (on the left) is that this board and its software are designed to operate on Windows PCs. The screen image shown is typical of what you'll use to control the module.

However, you can write your own software for other platforms, as long as the platform communicates using the Internet Protocol's TCP/IP.

If a PC controls the module, you must have access to a UDP/IP (un-numbered datagram; connectionless) socket to communicate with the module. The Winsock control in Windows provides that communication; other operating systems have different methods of programming network sockets.

The EtherI/O24 module includes IP's DHCP (Dynamic Host Configuration Protocol) support so that it can automatically obtain its Internet Protocol address from a server. If a DHCP server isn't available, the module can be configured by jumper to a fixed address. That lets you do initial programming. Once programmed, the device can then have any IP address you assign. The non-volatile EEPROM mentioned in the press statement (1Kb in size) can be programmed to permit the module to have a fixed user-assigned IP address.

Automatic scanning

The EEPROM can also store data to let each of the module's ports power-up in a user-defined state, and/or to let it automatically scan any of its input lines at a user-defined rate. If un-configured, all ports are initially set as TTL inputs, with pull-ups disabled. Each of the unit's 24 signal lines also has an independent control bit that controls whether the module detects changes on that line.

The system can also digitally filter signals and transmit a UDP/IP packet to report any valid input line changes to a pre-programmed destination address. The module periodically scans any or all of its digital inputs. Filtering is done on a per port basis with each port filtered as a group. The lowpass filtering is used to remove noise.

In use, the module's I/O scan rate can be set from 1ms to 65.5s, and the filter can be set to discard any number of unstable readings from one up to 255. The automatic scanning lets changes of input signals to be sent to a host without the host having to poll the module.

Talking module-to-module

Using automatic scanning also permits one EtherI/O24 module to be connected directly to another EtherI/O24 module, either locally across an Ethernet connection, or even globally across the Internet. In that application, the states of the ports on one module can be sent to the other modulewithout a host system. Using this mode and two or more modules, several (even hundreds) of signals can be sent from one location to another. By using fiber optic converters, this distance can be extended dramatically.

The module also includes LEDs that can let you ascertain whether a module is powered, active, or in standby. The LEDs can also indicate whether any Ethernet signals are reaching the module. As all Ethernet switches also have link and activity LED indicators, that makes it easy to see if any parts of a network aren't communicating.

As each module has its own serial number, the control software is also able to verify that all parts of the network and all I/O modules are correctly communicating, and it can notify you of the location of a malfunction. Finally, the low cost per I/O line of the module supports monitoring of non-signaling inputs such as power supply rails.

The EtherI/O24 module should lend itself well to a variety of applications in data acquisition and control, automation, and test. In fact, its utility is pretty much limited by your imagination. This is a nifty product, especially so when you consider it's less-than-$100 price tag.

- Alex Mendelsohn


Article Comments - Less-than-$100 module puts TTL I/O o...
*? You can enter [0] more charecters.
*Verify code:


Visit Asia Webinars to learn about the latest in technology and get practical design tips.

Back to Top