In Control

I just got asked about how many devices can be supported on a ModBus link. There is much confusion around such questions, so here's a quick summary of the facts.

ModBus is a protocol. It defines messages, responses and data content. It is the language. It says nothing about the communications interface (lips, tongue, vocal chords). Other protocols include TCP, X-modem and Morse code. (If you are knowledgeable enough to debate me on the latter, you probably don't need to be reading this :-)

RS232 is a communications interface. The RS232 standard defines some electrical voltage and current levels. It says nothing about the language (including nothing about the number of bits, parity etc., which strictly speaking are the character profile, something else again. Phonemes?)

RS485 is another electrical interface. So are RS422, Ethernet, current loop, V35 etc.

So maybe now you can see why questions like "do you have a ModBus interface" or "do you have RS485 protocol" are not the right question to ask.

So how many widgets can I connect?

We have just written a new support program, primarily for SPLat OEM customer. It is a small utility program that makes it easy to download already translated SPLat programs ("SPLatWare") into a board. If you sell equipment containing a SPLat, and you want an easy way for your customers to update the program, this is the tool to do it with. It is much easier than using SPLat/PC, and allows you to keep your source code secret.
You can access SPDownLoad here.

Our website now features a new "Take the Tour" section for OEM. In 5 minutes this brief and to the point "slideshow" will give you an idea of how well a SPLat controller in your product would help make you more competitive. So if your product needs an electronic controller, why not Take the Tour now!

Rob wrote:

I have a programming/operational question as follows; My machine has a vacuum arm which contacts an empty bag and picks it up. The vacuum arm has a spring-loaded micro switch on it (normally open) which, when it contacts the bag, closes (an input). This causes the vacuum arm to reverse and now the spring loaded micro switch is, physically (open), OFF.

From a programming view, do I still need to tell the controller that the switch is OFF (open) in order for it to be used again (eg. waiton) as an input to do a different function??

This may sound like a stupid question but it is to clear up what is physically going on versus what the controller believes is the state of an input.

We have a program on Australia's national TV broadcaster the ABC, called The New Inventors. A remarkable "first" happened tonight. One of our customers, Brian Gay, became the first inventor to appear twice with his inventions. And both his inventions rely on SPLat controllers!.

The first invention appeared about a year ago. It is called Suspense and is an kind of aquatic exercise tank.

The other invention, featured on TV tonight, is Brian's water conservation shower, Quench. The Quench shower uses a unique recirculation system to allow you to take long, hot showers without squandering vast amounts of water, and with an saving in energy of up to 70% or more. Quench won the Housing Industries Association "2007 Best new product award".

".. SPLat Controls is a sound company with highly professional engineering and excellent quality production. Their contribution to the success of our companies has been most significant." - Brian Gay, HydroCo, Australia

You can see movies of both these products in action.

Projects using SPLat have been featured on TV twice this week! The day before yesterday it was Brian Gay's watery inventions. Last night it was the new Melbourne City Council office building, known as CH2. It was featured on Catalyst, a weekly, highly regarded science show on ABC, our national broadcaster.

CH2 is an amazing office building that works with the environment rather than against it. It uses about 85% less energy and 70% less water than conventional office buildings. Architect Mick Pearce looked to termites for inspiration for the HVAC design of the building. Termites keep their nests at around 30°C (85°F) - despite outside temperatures varying between 40°C (105°F) in the day and below freezing at night. Pearce uses a whole array of methods to make the building thermally efficient, including intelligent opening and closing of windows to make maximum use of natural air movement and cooling.

If you want to write a ModBus master program for the PC, using .NET, this may be for you.

Kelly wrote:

Hi David

I'm converting some older code to multitask.

In subroutines where I have used PAUSE or similar, can I just use the
supertimer and do I need to have all "yieldtask" instructions in the
task itself ?

Kelly wrote further:

In the example below with a star delta type setup, where there is Pause instruction in the subroutine which is illegal. I guess I would have to move the StarDeltaStart subroutine into the Task1 routine itself.

LaunchTask      Task1
LaunchTask      Task2

Task1
 yieldtask      
 gosub  StarDeltaStart
 goto   Task1

StarDeltaStart
 on     StarRelay
 pause  200
 Off    StarRelay
 pause  50
 on DeltaRelay
 return

Dean wrote:

How can CC16's be connected to a RS485 network?