We’re now making our marks on a spanking new year. Like carving the morning’s first run in fresh powder, or - for the indoor types - making your first mark in a new jar of Nutella.
There sure is lots of change coming in ’09. New economic prophesies, new President, new bailouts and apparently a new Ice Age here in the frozen Illinois plains.
Lots of new, lots of change. As Churchill said, “There is nothing wrong with change, if it is in the right direction.”
But what won’t change in ’09?
- The US still won’t adopt the metric system
Lindsay Lohan will still be the party girl that used to be an actress
And Modbus will continue to bridge the technology gaps between the automation equipment of the twenty and twenty first century.
What made Modbus the de facto standard – the common denominator among hundreds of communications choices?
- It’s thin and simple. It takes very little hardware and is easy to learn. Days, not months.
- It typically uses RS-232, RS-485 and Ethernet as a physical layer. Sweet.
- Modbus is designed to move raw data, regardless of function, making it flexible for vendors to implement in a wide variety of apps.
- It’s free. No license, no royalties. Only barrier to entry is downloading the pdf specification.
Last month I intruded on your eggnog and shared a thimble-full of Modbus info. Today let’s get past the smooth surface and talk about the top 5 Modbus problems – and how to solve them.
First, recall the three Modbus flavors.
- Modbus ASCII. Communicating over 232 or 485, ASCII is ultra simple, human readable, 7 data bits, but not horribly efficient.
- Modbus RTU. Also over 232 or 485, with 8 data bits and better error checking, RTU is much more bus-efficient than ASCII, but also more sensitive to timing.
- Modbus/TCP, which nicely wraps Modbus packets for use over Ethernet, delivering all the speed and networking benefits of TCP/IP.
Sounds slick from the 5000 foot view. So what turbulence lies under the surface?
Classical serial port problems. You’ve got 5 devices on your Modbus port hardcoded to 9600 baud and your boss just handed you a shiny new box that some newbie engineer decided to hardcode at 19,200 ‘cuz it’s faster. Your face sinks like a kid on Christmas with a new cell phone without unlimited texting. What to do?
Or you’ve only got one available 485 port on your controller to talk to your five Modbus slave devices. But four of them are RTU and one is ASCII. Crud.
Your problems may lurk in murkier water. You’ve been tasked with adding some monitoring software to your four Modbus-controlled production lines but find that each of the four lines uses identical Modbus addresses. Ouch!
Here’s an even better one. Your boss has asked you to connect another Modbus master to your Fig Newton line so he can monitor fig yield from his winter home in Boca. Everything works great until Mr. Pointy-Hair Technowiz finds the setting to crank up the polling rate to 10 milliseconds, crashing your Modbus controller and sending figs flying (hence the often misquoted adage, “when figs fly”).
New Purchasing guy gets a wild hair and decides that he’s switching to the “-E” option on the new controllers because surely the entire plant is Ethernet by now – leaving you with a truckload of installed Modbus RTU slaves and no 485 port. Yeesh.
So what are you, the lone voice of engineering reason, to do in face of multitudes of potential Modbus woes? Don’t fret – I now have the answer.
From the clandestine engineering labs of B&B Electronics, secreted in the frigid tundra of Illinois, we’ve just released the solution to all of life’s Modbus problems – the new Vlinx™ MESR series Modbus Gateway.
Bottom line, beneath all the marketing fluff, here’s what the new Vlinx™ MESR series can do:
- Convert between ASCII, RTU and TCP – master or slave.
- Convert serial settings – baud rate, 232/485, stop bits – making any Modbus serial device play nice with its peers.
- Remap Modbus ID’s on the fly – powerful stuff – you’ll never have another address conflict
- Prioritize traffic from multi-master systems – prioritize by function code, Modbus ID or IP address to be sure the most important requests from the most important masters are handled first.
- Built-in Fiber Optic Ethernet options for long-distance, high immunity Modbus/TCP runs.
Check it out - http://bb-europe.com/product_multi_family.asp?MultiFamilyId=86
Happy (Modbus) Connections,
+353 91 792444