I need help,does someone have information about RS242 and RS485 communication?
Thank you
Answer:
There is a lot of information on the web. Just "google" RS232 or RS485.
RS232 (EIA232) is a point to point serial communication "standard". It is normally used in applications under 50 feet. Aside from the 3 communication lines used in the standard, there are a number of handshaking signals that can sometimes pass between devices communicating using RS232. There are two types of devices defined in the standard (DTE and DCE). Data Terminal Equipment is a device such as a computer. Data Communication Equipment is a device like a modem. The normal practice is to connect a DTE and a DCE together with a "straight" cable. When two DTE'S need to communicate, something called a null cable or null modem cable is used to "hook" them together. Transmit and receive will be reversed on one end of the cable, otherwise TX would be connected to TX and RX would be connected to RX and the two DTE'S would not "talk". Depending on the two devices, handshaking may be required. The easiest way to do this with DTE'S talking to DTE'S is to short RTS to CTS on the connector going to the device that needs the handshaking (When the DTE "asks" for Request to Send, it is looped bake and looks like Clear to Send from a DCE). Two DCE'S can be made to communicate using similar methods, although it is normally more of a chore. All of this information is available on the WEB, explained I am sure much better than I can explain it.
RS485 is a multi-drop standard. It has a range of about 4000 feet if I remember right. It can be either two wire or four wire and is supposed to be terminated on the last device with a resistor having the characteristic impedance of the cable pairs used to transport the signal. It just happens that CAT 5 cable is a pretty good choice for the RS485 signal. I do not believe there is a printed standard impedance for RS485 but there is for RS422 (122 ohms if I remember correctly). RS422 is very similar to RS485, but is not multi-drop. You can have up to 32 receivers on the RS485 communications loop.
If you have any specific questions on either of these standards, post a question, and maybe I will see it.
I have many hours, or more like weeks getting devices to communicate using these two methods and others. If you have a specific question, I might be able to help.
Somehow, for what is supposed to be "simple" standards, it can be very confusing.
I've never heard of RS242, are you sure it's not RS232?
RS232 uses at least 3 wires (RX,TX and ground), is used for short distances, and uses voltages in the range of -12V to +12V.
RS485 is used for relatively long distance (longer than RS232) communication, but at lower speeds (up to 100Kbps) and can use only two wires to communicate (uses differential voltage), although you should ground each terminal carefully. I've used RS485 to communicate on 1km wires with no problems.
Look at these links for more info:
http://en.wikipedia.org/wiki/rs-485...
http://en.wikipedia.org/wiki/rs-232...
I think you mean RS422. RS422 is a 5V differential standard. In an asynchronous system it uses two wires for transmit data and two wires for receive data. In synchronous data systems, it will have a pair of wires for tx clock and another pair for rx clock as well. Of course, it also has a shield. RS422 is a point to point electrical interface. meaning it connects betweet two devices.
The RS485 voltage levels are identical to RS422, except that RS485 (as mentioned by a previous responder) can be used in a mult-drop system. There are variants of the RS485. Full duplex, and half duplex. The full duplex uses two wires in a bidirectional fashion. Timing is critical to avoid collisions. The half duplex RS485 uses 2 wires for tx and 2 wires for RX. The difference from RS-485 is that the transmitter can be tri-stated to allow multiple transmitters to be connected. Only one transmitter can talk on the line at a time. So the protocol must remove any ambiguity as to who should be driving the bus at any given time.
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