![]() ![]() The signal path is differential, and handles bit rates above 50Mbps. ![]() It specifies a single driver with multiple receivers. RS-422 is a unidirectional, full-duplex standard for electrically noisy industrial environments. Any RS-232 system must accommodate these constraints. Other RS-232 specifications include nominal ±5V transmit and ☓V receive (space/mark) signal levels, 2V common-mode rejection, 2200pF maximum cable load capacitance, 300Ω maximum driver output resistance, 3kΩ minimum receiver (load) impedance, and 100ft (typical) maximum cable length. It provided a single-ended channel with baud rates up to 20kbps, and later enhanced to 1Mbps. RS-232 is a standard that originated as a communications guide for modems, printers, and other PC peripherals. What is RS-485? How does it compare to other serial protocols, and for what applications are they best suited? The following overview compares the characteristics and capabilities of the RS-485 PHY with those of RS-232 and RS-422. Throughout this application note, we will use the "RS" nomenclature to refer to the respective ANSI EIA/TIA standards. It also shows the ways that you can optimize data rates as a function of cabling, system design, and component selection. This article focuses on the RS-485 (EIA/TIA-485) protocol and the applications best suited to that standard. Though each protocol suits a particular application, in all cases you must consider cost and performance of the physical (PHY) layer. The various serial-datacom protocols range from RS-232 (EIA/TIA-232) to Gigabit Ethernet, and beyond. This application note shows how to go farther and faster. However, Maxim has raised the performance of RS-485 to 100Mbps with the introduction of products such as the MAX22500E. So, the crucial question is: How far can you reliably transmit and receive data at a specified data rate? The original publishing of this application note used the MAX3469 to demonstrate RS-485 performance, and that data is still valid. ![]() Designers of industrial datacom systems often ask, What data rates can be reliably achieved over what distance, and how? The design trade-off has always been less distance at a higher rate, or greater distance at a lower rate. ![]()
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