# MAX232

> Mediated Wiki article. Canonical URL: https://mediated.wiki/source/MAX232
> Markdown URL: https://mediated.wiki/source/MAX232.md
> Source: https://en.wikipedia.org/wiki/MAX232
> Source revision: 1346896113
> License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/)

1987 integrated circuit

MAX232 chip in [DIP-16](/source/Dual_in-line_package) package

The die of a MAX232

MAX232 pinout: Red: power, Yellow: [charge pump](/source/Charge_pump) capacitors,
Blue: outputs, Green: inputs,
Pins 9–12: TTL/CMOS I/O voltages

The **MAX232** is an [integrated circuit](/source/Integrated_circuit) by [Maxim Integrated Products](/source/Maxim_Integrated_Products), now a subsidiary of [Analog Devices](/source/Analog_Devices), that converts signals from a [TIA-232](/source/RS-232) (RS-232) serial port to signals suitable for use in [TTL](/source/Transistor-transistor_logic)-compatible digital logic circuits. The MAX232 is a dual transmitter / dual receiver that typically is used to convert the RX, TX, CTS, RTS signals.[1]

The drivers provide TIA-232 voltage level outputs (about ±7.5 [volts](/source/Volt)) from a single 5-volt supply by on-chip [charge pumps](/source/Charge_pump) and external [capacitors](/source/Capacitor). 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 [TTL](/source/Transistor-transistor_logic) levels.[1] These receivers have a typical threshold of 1.3 volts and a typical [hysteresis](/source/Hysteresis) of 0.5 volts.[1]

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,[2] and MC1489 quad receiver chip required 5 volt power.[3] 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](/source/Charlie_Allen_(engineer)) and designed by [Dave Bingham](/source/Dave_Bingham_(engineer)).[4][5][6] [Maxim Integrated Products](/source/Maxim_Integrated_Products) announced the MAX232 no later than 1986.[1]

## Versions

The later MAX232A is [backward compatible](/source/Backward_compatibility) with the original MAX232 but may operate at higher [baud](/source/Baud) rates and can use smaller external capacitors – 0.1 [μF](/source/Farad) in place of the 1.0 μF capacitors used with the original device.[7] The newer MAX3232 and MAX3232E are also backwards compatible, but operates at a broader voltage range, from 3 to 5.5 V.[8][9]

Pin-to-pin compatible versions from other manufacturers are ICL232, SP232, ST232, ADM232 and HIN232. [Texas Instruments](/source/Texas_Instruments) makes compatible chips, using MAX232 as the part number.

## Voltage levels

Main article: [RS-232](/source/RS-232)

The MAX232 translates a TTL logic 0 input to between +3 and +15 V, and changes TTL logic 1 input to between −3 and −15 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](/source/RS-232#Voltage_levels).)

TIA-232 line type and logic level TIA-232 voltage TTL voltage to/from MAX232 Data transmission (Rx/Tx) logic 0 +3 V to +15 V 0 V Data transmission (Rx/Tx) logic 1 −3 V to −15 V 5 V Control signals (RTS/CTS/DTR/DSR) logic 0 −3 V to −15 V 5 V Control signals (RTS/CTS/DTR/DSR) logic 1 +3 V to +15 V 0 V

## Applications

TIA-232 to TTL converters that use MAX232

Main articles: [Serial port](/source/Serial_port) and [TTL serial](/source/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 V ([RS-422](/source/RS-422) and [RS-485](/source/RS-485)) and single-ended RS-232 albeit at reduced voltage.

## References

1. ^ [***a***](#cite_ref-Electronics_19860724_1-0) [***b***](#cite_ref-Electronics_19860724_1-1) [***c***](#cite_ref-Electronics_19860724_1-2) [***d***](#cite_ref-Electronics_19860724_1-3) ["At Last, It's Easy To Design RS-232-C Modems"](https://worldradiohistory.com/Archive-Electronics/80s/86/Electronics-1986-07-24.pdf#search=%22max232%22) (PDF). *Electronics*: 89–92. 1986-07-24.

1. **[^](#cite_ref-TI_MC1488_2-0)** [MC1488 (MC1488, SN55188, SN75188) product webpage; Texas Instruments.](http://www.ti.com/product/MC1488)

1. **[^](#cite_ref-TI_MC1489_3-0)** [MC1489 (MC1489, MC1489A, SN55189, SN55189A, SN75189, SN75189A) product webpage; Texas Instruments.](http://www.ti.com/product/MC1489)

1. **[^](#cite_ref-EDN_1997_4-0)** EDN Staff, ed. (1997-05-08). ["EDN's 1996 Innovator / Innovation Competition"](https://www.edn.com/edn-access-05-08-97-edns-1996-innovator-innovation-competition/). *[EDN](/source/EDN_(magazine))*. [Archived](https://web.archive.org/web/20211210184016/https://www.edn.com/edn-access-05-08-97-edns-1996-innovator-innovation-competition/) from the original on 2021-12-10. Retrieved 2021-12-10.

1. **[^](#cite_ref-Sherman_2016_5-0)** Sherman, Len (2016-12-16). ["Almost 30 years of the MAX232"](https://www.bisinfotech.com/almost-30-years-of-the-max232/). *BISinfotech*. [Archived](https://web.archive.org/web/20211210030033/https://www.bisinfotech.com/almost-30-years-of-the-max232/) from the original on 2021-12-10. Retrieved 2021-12-10. The MAX232's success was as much a tribute to the vision of its definer, [Charlie Allen](/source/Charlie_Allen_(engineer)), as it was to the ingenuity of its designer, [Dave Bingham](/source/Dave_Bingham_(engineer)).

1. **[^](#cite_ref-Fox_2021_6-0)** Fox, Brett J. (2021). ["What Makes Your Great Engineers Great?"](https://www.brettjfox.com/what-makes-your-great-engineers-great/). [Archived](https://web.archive.org/web/20211210030933/https://www.brettjfox.com/what-makes-your-great-engineers-great/) from the original on 2021-12-10. Retrieved 2021-12-10. The launch of the MAX232 family is particularly insightful. [Charlie Allen](/source/Charlie_Allen_(engineer)), a brilliant, customer focused, applications engineer, noticed that our customers were using a product called the ICL7660, which [Dave](/source/Dave_Bingham_(engineer)) [Bingham] also designed, to provide the negative power supply for [RS-232](/source/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.

1. **[^](#cite_ref-Maxim_MAX232_7-0)** [MAX232 (MAX220 to MAX249) product webpage; Maxim.](https://www.maximintegrated.com/en/products/interface/transceivers/MAX232.html)

1. **[^](#cite_ref-Maxim_MAX3232_8-0)** [MAX3232 (MAX3222 to MAX3241) product webpage; Maxim.](https://www.maximintegrated.com/en/products/interface/transceivers/MAX3232.html)

1. **[^](#cite_ref-Maxim_MAX3232E_9-0)** [MAX3232E (MAX3222E to MAX3246E) product webpage; Maxim.](https://www.maximintegrated.com/en/products/interface/transceivers/MAX3232E.html)

Wikimedia Commons has media related to [MAX232](https://commons.wikimedia.org/wiki/Category:MAX232).

The Wikibook *[Serial Programming](https://en.wikibooks.org/wiki/Serial_Programming)* has a page on the topic of: ***[MAX232 Driver Receiver](https://en.wikibooks.org/wiki/Serial_Programming/MAX232_Driver_Receiver)***

---
Adapted from the Wikipedia article [MAX232](https://en.wikipedia.org/wiki/MAX232) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/MAX232?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.