9 Lives of RS-232 and RS-485
Dear Friend & Subscriber:
It was April 22, 2003 when I first reported on the death of RS-232. It wasn't exactly breaking news at the time. After all, the 1995 release of the USB 1.0 spec had the defenseless 232 port squarely in its crosshairs. But once again, as I've reported for each year since that dismal forecast in 2003, RS-232 is up. And its robust cousin, RS-485 is thriving.
Oops.
I'm not going to go into all the reasons why tried and true serial ports continue to thrive despite fierce growth and competition in the device connectivity business. You already know how the simplicity and flexibility of these serial workhorses makes them suitable for so many applications (in case you're enamored with the topic, stick around and read this all the way through).
But you and I haven't talked much about a silent partners-in-crime of the serial port. Perhaps more than any other single factor, this silent partner enabled the success of serial ports everywhere by creating a ubiquitous language and allowing multiple vendors equipment to carry on conversations on serial networks big and small. Modbus has been that silent partner.
Let's talk a bit about this unsung hero of protocols. Back in 1979, even as Skylab was plunging from the sky, folks over at Modicon developed a simple protocol for use between their PLC's and other factory equipment. To their credit, Modicon had the foresight to release Modbus as a public, royalty-free protocol. Today, nearly all industrial automation and instrumentation vendors include Modbus in their supported protocol list.
Just like RS-232 and RS-485, the strength of Modbus is in its simplicity, both for the user and the developer.
Want to read more? We've got a nice introductory paper on Modbus:
http://www.bb-elec.com/tech_articles/modbus_legacy.asp
And if you were looking for an opportunity to treat yourself to a shiny new 485 converter, we've got some that we specifically recommend for Modbus (u/c) applications.
DIN rail mount, double and triple isolated:
http://www.bb-elec.com/product_family.asp?FamilyId=302
Inline, isolated, I recommend the 4WSD9OTB:
http://www.bb-elec.com/product_family.asp?FamilyId=391
Inline, mini port powered converter - great for those field calls with your laptop - no power supply required. 485SD9TB
http://www.bb-elec.com/product_family.asp?FamilyId=15
And Modbus can go wireless too. Like to see a real life example of making a PLC work wirelessly using Modbus with the B&B Zlinx radio modems? Kelly, from our tech support team wrote up a real-world description on using the serial Modbus port to create a multidrop wireless connection between IDEC PLC's.
http://www.bb-elec.com/bb-elec/literature/tech/HookingUp3Zlinx_4107.pdf
Happy connections,
Mike Fahrion
(815)433-5100
support@bb-elec.com
P.S. Sometimes I mistakenly assume that the grey hairs on serial ports imply that all of you already know everything you want to about them. Many of you have reminded me (repeatedly) that I'm wrong and you'd like more training and info on how to work with RS-232 and RS-485. Would you like to see a webinar on the topic? Do you have a team that needs on-site training? Everything is fair game - let me know what you would like to see!
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