What is ttl and how does it relate to rs232 Document Transcript
What is TTL and How Does it Relate to RS232?Most people who are at least somewhat technically inclined know what USB, Ethernet and RS232are and perhaps even how they work. A good percentage of them also know of RS422 and RS485and how those standards relate to RS232. Many have used converters when dealing with thoseserial standards. Whats amazing is that comparatively few know what TTL stands for, and what ismeant by TTL communication and TTL devices. To be honest, unless youre an electrical engineer or hobbyist, information on TTL is not that easy to come by. If you look it up you actually find two definitions for TTL, both referring to data communication. One is "Time to Live" and refers to a data field in the Internet Protocol that indicates how many more hops a data packet will travel on the Internet before it is returned or discarded. A second one, and the one were interested in, is "Transistor-Transistor Logic" but even thatrequires extra explanation.Transistor-Transistor Logic, or TTL, refers to a way of constructing digital circuits. It was inventedin the early 1960s when first Sylvania and then Texas Instruments created TTL-based integratedcircuits. In TTL circuits, there are two transistors responsible for driving chip output, one of themgenerating the logical zero and the other the logical one. With TTL, a logical "zero" is defined asground (or usually 0 to 0.4 Volts), and a logic "one" as plus 5 Volt. That made a lot of sense sinceit is simple and microcontrollers are usually run on a single supply voltage.CLICK HERE TO GET INSTANT ACCESS TO CIRCUIT PROTOCOLSDownload this document if link is not clickableRS232, on the other hand, defines a logic "zero" as larger than plus three Volts and a logic "one"as less than minus 3 Volt. Voltages around zero, which is usually ground, are not considered asignal at all. Why use positive and negative voltages when circuits are natively generating eithera voltage or no voltage? Because signal degradation and interference are much more likely torender a TTL signal unusable than a RS-232 signal where a "one" is very clearly negative and a"zero" very clearly positive. This means that TTL signals are generally used for fastcommunication within a device whereas RS232 signals are used for slower external connectionsover longer distances.
Do note that there is a difference between actual TTL circuits, and using the term "TTL" to simplyrefer to the voltage levels used for communication. "TTL" communication can happen without anyactual TTL circuits or devices present.Anyway, you can see the difference between TTL and RS232 now: one is based on signalsgenerated by a certain type of integrated circuit, the other refers to signals that are specificallydefined for reliable data communication.Equally clear should be the need for a converter when youre dealing with both standards.Voltages need to be properly "translated" between the standards. More precisely, signals rangingfrom ground to 5 Volts must be translated into signals that can be up to plus or minus 10 Volts.That requires additional power sources and voltage inverter circuitry. Modern converters usuallydont need an external power supply as they are powered by the RS232 data lines themselves.Also note that serial to TTL adapters are available between RS232 and TTL as well as RS485 toTTL, and that TTL devices can be 3.3 Volt or 5 Volt, so make sure you get the proper converter.CLICK HERE TO GET INSTANT ACCESS TO CIRCUIT PROTOCOLSDownload this document if link is not clickableArticle source = ezinearticles.com/?What-is-TTL-and-How-Does-it-Relate-to-RS232?