Editing RS-232 (section)

==Related standards==
Other serial signaling standards may not interoperate with standard-compliant RS-232 ports. For example, using the [[TTL serial|TTL level]]s of near +5&nbsp;V and 0&nbsp;V puts the mark level in the undefined area of the standard. Such levels are sometimes used with {{nowrap|[[NMEA 0183]]-compliant}} [[GPS]] receivers and [[fishfinder|depth finder]]s. A chip such as [[MAX232]] is required to convert the voltage levels.

A 20&nbsp;mA [[digital current loop interface|current loop]] uses the absence of 20&nbsp;mA current for high, and the presence of current in the loop for low; this signaling method is often used for long-distance and [[opto-isolator|optically isolated]] links. Connection of a current-loop device to a compliant RS-232 port requires a level translator. Current-loop devices can supply voltages in excess of the must-withstand voltage limits of a compliant device. The original IBM PC serial port card implemented a 20&nbsp;mA current-loop interface, which was never emulated by other suppliers of [[plug-compatible]] equipment.

Other serial interfaces similar to RS-232:
*[[RS-422]] – a high-speed system similar to RS-232 but with [[differential signaling]]
*[[RS-423]] – a high-speed system similar to RS-422 but with [[unbalanced signaling]]
*[[RS-449]] – a functional and mechanical interface that used RS-422 and RS-423 signals; never caught on like RS-232 and was withdrawn by the EIA
*[[RS-485]] – a descendant of RS-422 that can be used as a bus in multidrop configurations
*[[MIL-STD-188]] – a system like RS-232 but with better impedance and rise time control.  One very significant difference: RS-232 uses a positive voltage to indicate a 0 and a negative voltage to indicate a 1.  MIL-STD-188 uses a negative voltage for 0 and a positive voltage for a 1.
*[[EIA-530]] – a high-speed system using RS-422 or RS-423 electrical properties in an EIA-232 pinout configuration, thus combining the best of both; supersedes RS-449
*[[EIA/TIA-561]] – defines RS-232 pinouts for [[Modular connector#8P8C|eight-position, eight-contact (8P8C) modular connectors]] (which may be improperly called RJ45 connectors)
*[[EIA/TIA-562]] – low-voltage version of EIA/TIA-232
*TIA-574 – standardizes the 9-pin D-subminiature connector pinout for use with EIA-232 electrical signalling, as originated on the IBM PC/AT
*[[EIA/TIA-694]] – similar to TIA/EIA-232-F but with support for higher data rates up to {{nowrap|512 kbit/s}}

The [[International Telecommunication Union]] publishes standard ITR-R V.24 (formerly CCITT standard V.24), "List of Definitions for Interchange Circuits between Data Terminal Equipment (DTE) and Data Circuit-Terminating Equipment (DCE)" with circuit definitions compatible to those in EIA RS 232. V.24 does not specify signal levels or timing. Electrical parameters for signals are specified in ITU-R-V.28.