What is meant by serial communiction using rs 232c

RS-232C (Recommended Standard 232, revision C) is an old (in computer terms) standard for communicating between a computer and a device, or between two computers, etc. It's a standard that defines the connectors, wiring, and some of the communication parameters that must be set in order to succeed.

RS-232C is now EIA-232, but most people still call it "RS-232". Here's a Wikipedia article on it.

RS-232 - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/RS-232)

Although it's now considered "obsolete", it's still extremely common in industry. Years ago, it was not as "standard" as it is now (companies implemented it differently). Nowadays, it's very standard.

When you use RS-232, you need to specify the Baud Rate, Data Bits, Stop Bits, and Parity as well as a type of handshaking (that can be "none"). It can be pretty complicated. The Wikipedia article describes it pretty thoroughly.

Many PCs still have a nine-pin connector (popularly referred to as a "DB-9" connector) that can implement RS-232C between the computer and another device. Older computers had a DB-25 connector that was used for the same purpose.

D-subminiature - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/D-subminiature)

The DB-25 connector actually had pins for at least two distinct types of communication (synchronous and asynchronous). Almost no one uses synchronous communication using RS-232c. It's all Asynchronous.

What is meant by networking?

Perito:

I'm going to confuse you a bit: D-subminiature - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/D-subminiature)

The DB-9 is like the band-aid; It really is a DE-9, but no one calls it that except when you want to buy them.

You title has already answered your own question..

Just to throw it out there, did you guys ever use the 6-pin (mini) DIN connectors?

All mini now, but the older computers were huge. Could never find the right plug. I use the mini's now all the time in video wiring, funny how they are kind of outdated as well, however, they are standard for Power/Video/Audio connections.

Yeah, basically PC's communicating.

When you go on the internet, you join a very large network, and every site you access is information you had sent from you over the network from another PC.

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I've merged these two threads since these appear to be from the same person.

Let me kind of add something.

Back in the day, all 25 pins were used; now just a small subset.
There were Data Terminal Devices (DTE) and Data something or other DCE or modems.

The signals had largely the same function, but modems did not call terminals.

You had two signals that said the devices had power. No point communicaing of they were not on.

You had 2 signals that said, I'm ready to communicate. These sigals could be dropped and re-asserted when hardware flow was enabled.

You had tranmit data and receive data which were lines that communication happened from.

There was a protective ground and a signal ground connection.

Then there was RI or ring indicatior.

SO the communication went something like this:

If the modem had power, it would asserty DTR.

There would be an incoming call which would assert RI (Ringng)

Modem would assert RTS (Request to send) It answered the phone.

Some handshaing would occur and the terminal would assert Clear to send

Data would occur over Tx/Rx/Gnd for the remainder of the transmission.

CTS/RTS would be the basis of hardware flow, ^S and ^Q would be the basis of software flow control.

A control-S would stop the paper tape reader and an ^Q would resume it.

These designations also carried over to video terminals.

The levels were -3 to -25 V and +3 tp +25 V

The standard was later really mucked up by IBM and used a 9 pin rather than a 25 pin connector and nobody followed the standard. Now levels have gone to about +-12V max and some systems use +-5V creating some havoc with devices.

RS422 made the communication differential. In may cases RS422 can be converted into RS232 with some wire juggleing.

RS485 came along which is a master/slave communication with about 32 devices and differential communication.

You really don't want to know about that serial communication era.

Back in the day, all 25 pins were used; now just a small subset.
There were Data Terminal Devices (DTE) and Data something or other DCE or modems.


That's not quite true. Even when 232 came out, people used either the asynchronous pins or the synchronous pins, not both. I don't think I ever saw a situation where they used both the synchronous and asynchronous sets of pins. There were actually very, very few cases where the synchronous pins were used -- just in extrremely specialized applications.

The DB-9 (DE-9) came out when IBM realized that there was no need for the synchronous pins.



... some systems use +-5V creating some havoc with devices.


There were some companies that used TTL voltages (0 and +5 V -- not understanding the standard). They claimed to adhere to "RS-232", but they weren't. That caused additional problems.



You really don't want to know about that serial communication era.


You hit that nail right on the head.

Just to throw it out there, did you guys ever use the 6-pin (mini) DIN connectors?


Yes. I've used them all -- and some that weren't allowed by the standard.

Our company used a DB-9 before the DB-9 specification appeared. The problem was that they used pins 2, 3, and 7 (data leads only) the same as the DB-25 (the DB-9 spec would have used pins 3, 2, and 5 respectively). That turned out to be a pain many years later. We were constantly having to make adapter cables.

Yea. A sysnchonous, ttwo asynchrounous (one normal and a back channel)

So, there were two asynchonous and one synchonous protocol. The low baud rate async was used to support the synchronous communication.

The synchonous mode was used for higher speed communications which most could not afford. Like satellite offices communicating with corporate offices.

We used it as a mux, to get across toll areas within the state.

This was when 1200 baud was FAST and expensive and 9600 didn't exist for phone lines. 300 baud was the norm.

Adapter cables were the norm. Then there eis the RJ-45 standard. Neat actually. A cross connection would change it to a DTE or vice versa. NO ring indicator, I believe.

Thanks Perito for the comments. We have lots in common, you know and a Merry Christmas too.