RS232

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chava
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RS232

Post by chava » Thu Oct 02, 2003 12:46 pm

Hi,
I have the protocol of the RS232 infront of me, but I cannot seem to anderstand something:
does DTE means a dumb device or DCE?
I have a device who knows how to communicate by RS232 ( USART) and I want to connect it to the PC. should I use stragth or crossed cable?? Im confused
someone told me once stragth and someone else told me crossed.....
??????
Jukin Chava<p>E.Dove Israel
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Chris Foley
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Re: RS232

Post by Chris Foley » Thu Oct 02, 2003 1:28 pm

RS-232 Tutorial<p>Usually, you either use a straight-thru or null modem-type cable. Both are commercially available, but the pinout is in the tutorial if you want to roll your own. You have a large safety margin on RS-232, and you shouldn't worry about incorrectly hooking anything that's RS-232 up (at least for a few minutes -- if you leave outie hooked up to outie permanently, you might cause some damage). Read the equipment manual, too. If those three don't work, get or make an RS-232 breakout box, and run through the other options on the tutorial page above. Start with no handshaking, and go from there. Call the manufacturer of the instrument or serial device for suggestions. Use a terminal program (like Hyper-Terminal in Win) to check comm first -- it might be your software. If your scope is warmed up, you also might want to look at what's going on at the instrument/serial device "outie" pins.<p>RS-232 isn't user-friendly, but it usually won't smoke your equipment if something is hooked up wrong. Eventually, you have to learn about it the way most of us did -- just try different things, and see if they work.<p>Good luck.
Chris<p>[ October 02, 2003: Message edited by: Chris Foley ]</p>

chava
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Re: RS232

Post by chava » Thu Oct 02, 2003 2:55 pm

Thanks
Jukin Chava<p>E.Dove Israel
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rshayes
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Re: RS232

Post by rshayes » Thu Oct 02, 2003 9:18 pm

If you have the actual RS-232 specification, I am not suprised that you do not understand it. It is one of the most incomphrensible documents ever written in the English language.<p>The original purpose of RS-232 was to define the interface between computers and modems on one end and modems and peripheral equipment on the other end. The modems were referred to as Data Communications Equipment (DCE) and the computer or other equipment was referred to as Data Terminal Equipment (DTE).<p>If two pieces of DTE are connected together, both devices have their output signals on similar pins. The input signals are also on similar pins. This conflict is resolved by using a "crossover cable", which connects the input pins on one end to output pins on the other end.<p>Equipment which is meant to be connected to a computer, such as a printer, is usually wired as DCE, so that a crossover cable will not be required. A link between two computers, which are both DTE, will require a crossover cable.<p>RS-232 also includes electrical specifications that are designed to be tolerant of erroneous connections. The outputs are supposed to be current limited. This limits the speed of the interface when long lines are used. The inputs usually incorporate series resistors to limit the current to acceptable values even if a signal lead is shorted to either a plus 15 volt or minus 15 volt supply.<p>RS-232 also includes several handshake signals. Most equipment usually uses only one or two of these. There is no standard for this. Radio Shack used to sell adapters that could be inserted between two pieces of equipment to correct these problems. The adapters used wire jumpers between two connectors so that practically any configuration could be implemented.

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