RS485, educate me please

[phantomcow2]

I am a little stumped by all of this. I only have a basic understanding of all these digital communication systems. Prior to a month ago, I thought it was parallel port or plug in the usb
I realize thats not the case now! So anyways, I have these motor drives that require some RS485 input. It only needs the RS485 input to configure the drive settings (current, microstepping, etc.). Past that, you control it through regular step and direction pulses, which is nice because I can use Mach or whatever else I want.

I really don't understand RS485, only that you can run the cables at much larger distances compared to RS232.
When one says RS485, is the only difference from RS232 the physical cable? Will I be able to use my computers 9 pin serial port to communicate with these RS485 input drives? I see these RS232 <--> RS485 converts around, but at two extremes of prices. On the lupper end I see thongs like this:
http://www.bb-elec.com/product_famil...e=Sub&Trail=12

On the bottom end I see this:
http://cgi.ebay.com/NEW-RS232-To-RS4...QQcmdZViewItem

Can somebody explain this to me?

[Al_The_Man]

The RS485 is a transmission hardware standard, as is RS232. If you are handy with building with ic's you can make one cheap, as the conversion IC's are plentifyll, Maxim should have, but at that ebay price it may not be worth going that route.
If you do a Google for RS485, there should be plenty of explanation sites.
B&B specialize in those products, they can be pricey, but they offer things like RS232 conversion for Allen-Bradly RS485 PLC's which are way lower than the OEM price.
Keep in mind that the RS485 is capable of much higher transmission rates, so if you convert, you have to be able to communicate at the lower RS232 rate.
Al.

[phantomcow2]

So is there any difference between hte converter on that ebay auction and the ones of the other link? Such a price difference makes me curious

[Al_The_Man]

I am sure electronically there is very little difference, to me the cost would be in the housing/connectors etc, the 2 or 3 IC's needed would probabally purchased in bulk for a few cents.
Al.

[phantomcow2]

I only need these for a couple minutes to allow setup for these drives (pasci). So as long as these can hold out that long, I am pleased. Is the RS485 cable physically different than the one labeled RS232 that I have already? I know I will have to solder my own connector for these to interface

[The Speaker Guy]

than RS232. RS485 Has lower EMI, and is less susceptible to EMI from other systems. It can also do multi drop, which RS232 can't do.

RS485 driver ICs are smaller and simpler than RS232.

Look on the web, beaucoup info on this

[Al_The_Man]

Originally Posted by phantomcow2 Is the RS485 cable physically different than the one labeled RS232 that I have already? I know I will have to solder my own connector for these to interface

For the short run on a bench just to set up you can use the same type of cable, just the connections are different. I assume you want to make one out of a RS232 cable?
Al.