TTL TO RS 232

Most logic-level signals are very weakly driven - both to conserve power and limit the amount of HF noise emitted.

So most logic-level signals are limited to short distances on the same PCB or in some cases maybe between two PCB boards with a very limited cable length between the boards.

To handle a bit longer distances, logic-level buffers may be used. This is common when interfacing medium-speed data between PCB. The buffer can supply higher currents but also often have rise- and fall-time limiters to reduce radiated HF energy. And the buffer normally has hysterese on the input to both support slow rise/fall times and to reject glitches from noise.

If the transfer rates are very high, then single-ended logic level can't be used any more, even for short distances between boards. So board-to-board communication normally need low voltage differential signalling (LVDS), where each digital line suddenly becomes two wires that flips polarity when the logic level changes.

For external cables, the amount of noise picked up can be quite significant. And also voltage differences beteen units that are separately powered. So RS-232 is a rather robust way to allow slow serial data up to about 15 meters. Logic level signal pins normally don't like that only one side of the connection is powered. This might break a chip. Or the unpowered chip may try to supply itself from the logic level input signal(s), which will put a significant load on the powered side.

So in the end, you normally always have specific buffer chips (often called transceivers since they transform transmitted and received signals between logic level and "long-distance capable" electrical formats) for signals leaving the PCB.

Most logic-level signals are very weakly driven - both to conserve power and limit the amount of HF noise emitted.

So most logic-level signals are limited to short distances on the same PCB or in some cases maybe between two PCB boards with a very limited cable length between the boards.

To handle a bit longer distances, logic-level buffers may be used. This is common when interfacing medium-speed data between PCB. The buffer can supply higher currents but also often have rise- and fall-time limiters to reduce radiated HF energy. And the buffer normally has hysterese on the input to both support slow rise/fall times and to reject glitches from noise.

If the transfer rates are very high, then single-ended logic level can't be used any more, even for short distances between boards. So board-to-board communication normally need low voltage differential signalling (LVDS), where each digital line suddenly becomes two wires that flips polarity when the logic level changes.

For external cables, the amount of noise picked up can be quite significant. And also voltage differences beteen units that are separately powered. So RS-232 is a rather robust way to allow slow serial data up to about 15 meters. Logic level signal pins normally don't like that only one side of the connection is powered. This might break a chip. Or the unpowered chip may try to supply itself from the logic level input signal(s), which will put a significant load on the powered side.

So in the end, you normally always have specific buffer chips (often called transceivers since they transform transmitted and received signals between logic level and "long-distance capable" electrical formats) for signals leaving the PCB.

The RS232 standard require certain voltage levels your micro can not produce www.radio-electronics.com/.../signals-voltages-levels.php

i use rs485

And some people use CAN.
And some people use USB.
And some people use FW.
And some people use Eth.
And some people use current loops.
And some people use fiber.
And some people use eSATA.
And some people use ...

There is an almost infinite number of different ways to make external signals more robust.

but i use RS485. it rocks.