View source for MAX232

{{short description|1987 integrated circuit}}
{{use dmy dates|date=December 2021|cs1-dates=y}}
{{use list-defined references|date=December 2021}}
[[File:Max232.jpg|thumb|MAX232 chip in [[Dual in-line package|DIP-16]] package]]
[[File:TI_2BC121M_MAX232N.jpg|thumb|upright|The die of a MAX232]]
[[File:MAX232 Pinout.svg|thumb|MAX232 pinout: Red: power, Yellow: [[charge pump]] capacitors,<br/>Blue: outputs, Green: inputs,<br/>Pins 9–12: TTL/CMOS I/O voltages]]
The '''MAX232''' is an [[integrated circuit]] by [[Maxim Integrated Products]], now a subsidiary of [[Analog Devices]], that converts signals from a [[RS-232|TIA-232]] (RS-232) serial port to signals suitable for use in [[Transistor-transistor logic|TTL]]-compatible digital logic circuits. The MAX232 is a dual transmitter / dual receiver that typically is used to convert the RX, TX, CTS, RTS signals.<ref name="Electronics_19860724"/>
The drivers provide TIA-232 voltage level outputs (about ±7.5&nbsp;[[volt]]s) from a single 5-volt supply by on-chip [[charge pump]]s and external [[capacitor]]s. This makes it useful for implementing TIA-232 in devices that otherwise do not need any other voltages. The receivers translates the TIA-232 input voltages (up to ±25 volts, though MAX232 supports up to ±30 volts) down to standard 5 volt [[transistor-transistor logic|TTL]] levels.<ref name="Electronics_19860724"/> These receivers have a typical threshold of 1.3 volts and a typical [[hysteresis]] of 0.5 volts.<ref name="Electronics_19860724"/>
The MAX232 replaced an older pair of chips MC1488 and MC1489 that performed similar RS-232 translation. The MC1488 quad transmitter chip required 12 volt and −12 volt power,<ref name="TI_MC1488"/> and MC1489 quad receiver chip required 5 volt power.<ref name="TI_MC1489"/> The main disadvantages of this older solution was the ±12 volt power requirement, only supported 5 volt digital logic, and two chips instead of one.
==History==
The MAX232 was proposed by [[Charlie Allen (engineer)|Charlie Allen]] and designed by [[Dave Bingham (engineer)|Dave Bingham]].<ref name="EDN_1997"/><ref name="Sherman_2016"/><ref name="Fox_2021"/>  [[Maxim Integrated Products]] announced the MAX232 no later than 1986.<ref name="Electronics_19860724">{{cite journal |title=At Last, It's Easy To Design RS-232-C Modems |journal=Electronics |date=July 24, 1986 |pages=89–92 |url=https://worldradiohistory.com/Archive-Electronics/80s/86/Electronics-1986-07-24.pdf#search=%22max232%22}}</ref>
==Versions==
The later MAX232A is [[backward compatibility|backward compatible]] with the original MAX232 but may operate at higher [[baud]] rates and can use smaller external capacitors{{snd}} 0.1&nbsp;[[Farad|μF]] in place of the 1.0&nbsp;μF capacitors used with the original device.<ref name="Maxim_MAX232"/> The newer MAX3232 and MAX3232E are also backwards compatible, but operates at a broader voltage range, from 3 to 5.5&nbsp;V.<ref name="Maxim_MAX3232"/><ref name="Maxim_MAX3232E"/>
Pin-to-pin compatible versions from other manufacturers are ICL232, SP232, ST232, ADM232 and HIN232. [[Texas Instruments]] makes compatible chips, using MAX232 as the part number.
==Voltage levels==
{{main|RS-232}}
The MAX232 translates a TTL logic 0 input to between +3 and +15&nbsp;V, and changes TTL logic 1 input to between −3 and −15&nbsp;V, and vice versa for converting from TIA-232 to TTL. (The TIA-232 uses opposite voltages for data and control lines, see [[RS-232#Voltage_levels|RS-232 voltage levels]].)
{| class="wikitable" border="1"shyam
|-
!  TIA-232 line type and logic level
!  TIA-232 voltage
!  TTL voltage to/from MAX232
|-
|  Data transmission (Rx/Tx) logic 0
|  +3&nbsp;V to +15&nbsp;V
|  0&nbsp;V
|-
|  Data transmission (Rx/Tx) logic 1
|  −3&nbsp;V to −15&nbsp;V
|  5&nbsp;V
|-
|  Control signals (RTS/CTS/DTR/DSR) logic 0
|  −3&nbsp;V to −15&nbsp;V
|  5&nbsp;V
|-
|  Control signals (RTS/CTS/DTR/DSR) logic 1
|  +3&nbsp;V to +15&nbsp;V
|  0&nbsp;V
|}
==Applications==
[[File:RS-232 to TTL converters using MAX232.jpg|thumb|TIA-232 to TTL converters that use MAX232]]
{{main|Serial port|TTL serial}}
The MAX232(A) has two receivers that convert from RS-232 to TTL voltage levels, and two drivers that convert from TTL logic to RS-232 voltage levels. As a result, only two out of all RS-232 signals can be converted in each direction. Typically, the first driver/receiver pair of the MAX232 is used for TX and RX signals, and the second one for CTS and RTS signals.
There are not enough drivers/receivers in the MAX232 to also connect the DTR, DSR, and DCD signals. Usually, these signals can be omitted when, for example, communicating with a PC's serial interface, or when special cables render them unnecessary. If the DTE requires these signals, a second MAX232 or some other IC from the MAX232 family can be used.
==Derivatives==
The MAX232 family was subsequently extended by Maxim to versions with four transmitters (the MAX234) and a version with four receivers and four transmitters (the MAX248), as well as several other combinations of receivers and transmitters. A notable addition is the MAX316x which is able to be electrically reconfigured between differential 5&nbsp;V (RS-422 and RS-485) and single-ended RS-232 albeit at reduced voltage.
==References==
{{Reflist|refs=
<ref name="Sherman_2016">{{cite web |title=Almost 30 years of the MAX232 |author-first=Len |author-last=Sherman |date=2016-12-16 |work=BISinfotech |url=https://www.bisinfotech.com/almost-30-years-of-the-max232/ |access-date=2021-12-10 |url-status=live |archive-url=https://web.archive.org/web/20211210030033/https://www.bisinfotech.com/almost-30-years-of-the-max232/ |archive-date=2021-12-10 |quote=The MAX232's success was as much a tribute to the vision of its definer, [[Charlie Allen (engineer)|Charlie Allen]], as it was to the ingenuity of its designer, [[Dave Bingham (engineer)|Dave Bingham]].}}</ref>
<ref name="Fox_2021">{{cite web |title=What Makes Your Great Engineers Great? |author-first=Brett J. |author-last=Fox |date=2021 |url=https://www.brettjfox.com/what-makes-your-great-engineers-great/ |access-date=2021-12-10 |url-status=live |archive-url=https://web.archive.org/web/20211210030933/https://www.brettjfox.com/what-makes-your-great-engineers-great/ |archive-date=2021-12-10 |quote=The launch of the MAX232 family is particularly insightful. [[Charlie Allen (engineer)|Charlie Allen]], a brilliant, customer focused, applications engineer, noticed that our customers were using a product called the ICL7660, which [[Dave Bingham (engineer)|Dave]] [Bingham] also designed, to provide the negative power supply for [[RS-232]] line drivers and receivers. So, Charlie approached Dave, and asked Dave if he could design an IC that integrated the functionality of the ICL7660 with an RS-232 line driver and receiver.}}</ref>
<ref name="TI_MC1488">[http://www.ti.com/product/MC1488 MC1488 (MC1488, SN55188, SN75188) product webpage; Texas Instruments.]</ref>
<ref name="TI_MC1489">[http://www.ti.com/product/MC1489 MC1489 (MC1489, MC1489A, SN55189, SN55189A, SN75189, SN75189A) product webpage; Texas Instruments.]</ref>
<ref name="Maxim_MAX232">[https://www.maximintegrated.com/en/products/interface/transceivers/MAX232.html MAX232 (MAX220 to MAX249) product webpage; Maxim.]</ref>
<ref name="Maxim_MAX3232">[https://www.maximintegrated.com/en/products/interface/transceivers/MAX3232.html MAX3232 (MAX3222 to MAX3241) product webpage; Maxim.]</ref>
<ref name="Maxim_MAX3232E">[https://www.maximintegrated.com/en/products/interface/transceivers/MAX3232E.html MAX3232E (MAX3222E to MAX3246E) product webpage; Maxim.]</ref>
<ref name="EDN_1997">{{cite web |title=EDN's 1996 Innovator / Innovation Competition |date=1997-05-08 |editor=EDN Staff |magazine=[[EDN (magazine)|EDN]] |url=https://www.edn.com/edn-access-05-08-97-edns-1996-innovator-innovation-competition/ |access-date=2021-12-10 |url-status=live |archive-url=https://web.archive.org/web/20211210184016/https://www.edn.com/edn-access-05-08-97-edns-1996-innovator-innovation-competition/ |archive-date=2021-12-10}}</ref>
}}
== External links ==
{{Commons category}}
{{Wikibooks|Serial Programming|MAX232 Driver Receiver}}
* [https://www.maximintegrated.com/en/products/interface/transceivers/MAX232.html MAX232 & MAX232A], Maxim
* [https://blog.heypete.com/2016/09/11/investigating-fake-max3232-ttl-to-rs-232-chips/ Investigating Fake MAX3232 TTL-to-RS-232 Chips]
[[Category:Integrated circuits]]