Serial Programming/RS-232

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Introduction

RS 232 is one of the oldest and simplest asynchronous communication standards used in the computer and electronics industries. It can support a number of communication methods including null modem, modem with handshake, etc.

History

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Physical Layer

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Requirements

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Limitations

Limitations of the RS-232 standard include:

Large voltage swings are required between the positive and negative supplies. This creates a high power demand and also limits the speed at which the interface can operate.
Use of a common earth or ground limits the length of the cable as the ground will degrade over distance.
There is no method for sending power to the connected device, although a small amount is available this is generally only sufficient for very low power devices (for example, a computer mouse). This limits the usefulness as every device must have its own independent power supply.
The connector is very large meaning all devices will be relatively large.

DTR/DSR Handshaking

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RS-232 in the Real World

--142.74.1.3 (discuss) 13:12, 8 August 2013 (UTC)

DE-9s and Other Lies

It's true-- there is no such thing as a 9-pin RS-232 serial device. So why do you seem to see this everywhere-- PCs and laptops, for example?

Well, primarily because of three reasons:

There often isn't enough room to put DB-25 connectors on everything.
Properly-shielded RS-232 cables are expensive and bulky.
Most of the signals "lost" in the DE-9 connector aren't really critical, and can be worked around.

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Physical Limitations in Practice

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If you're designing new hardware, please consider using RS-485 (Serial Programming:RS-485 Technical Manual) or Ethernet (____) rather than RS-232. The RS-485 hardware can communicate faster over longer distances than RS-232, and the hardware cost is usually less (2 wires instead of 3).
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