Serial communication questions

Posted on 2007-03-19
Medium Priority
Last Modified: 2013-11-13
I would like to find out more about serial communications, i have used them but i merely followed the instructions like which pin to which pin on the instructions manual. I would like to how the wiring works, why pin 2 to 3 and 3 to 2 etc and are the wiring a standard (same throughout for 232,422 and 485) what is half duplex and what is full duplex, where can i find wiring configurations for all the above and what is the handshaking for because i have never need to used it..most of the time i use rs232 and rs485 for matchine to computer interaction. What are the cables used for these because i have seen many type of cables in the market but i am always not sure which to get. thanks
Question by:jaxrpc
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nobus earned 2000 total points
ID: 18754815
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Expert Comment

ID: 18756705
A simplified way of beginning to understand the cabling between components starts with the designation of each type PC's are considered DTE's (Data Terminal Equipment) and  DCE's (Data Communication Equipment) are considered to be Modems and access points on wireless networks. Once you identify which type of component you have on each end of the cable, for example a PC to PC connection would require DTE wiring on each end of the cable, or a PC to modem  -DTE to DCE.
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Author Comment

ID: 18761883
hi, what kind of cables are used? are they same as power cables? they looked the same to me..how to differeniate them and what about ethernet cables when 25 pin to ethernet.
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Expert Comment

ID: 18762332
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Expert Comment

ID: 18762559
They certainly aren't power cables.  The serial cable is usually made up of 9- 24AWG wires  for db9 cables and 25 wires for db 25 cables. There is differences in capacitance for certain cables and that determines the length that a cable can run.It is set up as capacitance Per Foot. This article gives some info on the cable lengths and how to determine them.

This article delves into the serial to rj45(ethernet) cablng with wiring diagrams.

Expert Comment

ID: 18783938
Serial communication is pretty much history. It was used in the past to connect terminals and printers to host machines, such as unix based mainframes. Ethernet has replaced serial because it is faster and easier to configure. Serial was doomed when every manufacturer would have their own way of configuring their ports. ie some hardware would have transmit coming from pin 2 and some from pin 5. I used to wire mainframes with serial connections and I am happy to say I have not touched serial equipment in 10 years.
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Expert Comment

by:Arno Koster
ID: 19009044
Serial communication comes down to serially (opposite to parallel) sending zero's and one's from one device to the other. As of the serial nature (bit after bit) int theory one signal cable shoudl suffice but in general two signal cables are to be used, one to send and one to receive information. That's why for example pins 2  (transmit data) & 3 receive data) are to be connected crosswise : the sending device transmits to pin 2 which is to be connected to the listening device on pin 3. These wiring configurations can be found on wikipedia (eg. [http://en.wikipedia.org/wiki/RS-232] : par. 6)

Handshaking can be used to determine which device is able to send and wich should be listening. Some devices can talk and listen at the same time (full-duplex), some can listen or talk but only one of them at a time (half-duplex). This handshaking can be performed by software running on the communicating devices but is can also be done in hardware. For the latter case more pins need to be connected (DTR / DSR / RTS / CTS).

Expert Comment

ID: 19399546
I have to disagree with computerguy107 yes serial communication is not used much anymore in mainstream buissness or home equipment but it is still very much alive and critical to mobile Automated systems ie Codesys, twincat, or any IEC-61131 standard PLC, its the easiest and most reliable way to program the software for these plc's. I use a Serial Connection all most everyday at work. so yes its not a mainstream connection method anymore but dont for a minute think Serial Communication will just up and be gone one day - just had to say that  

Expert Comment

ID: 19614683
I agree with JJL088.
Parallel communication is easy to implement but it requires lots of wiring.
Sometimes you want to have a single slim data cord to make your wiring simple and nice...that is if you do not care about the transfer speed since miliseconds are not noticable...
Note: usb and RS232 are commonly used for serial communication

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