![MAX232 Pinout](https://upload.wikimedia.org/wikipedia/commons/5/53/MAX232_Pinout.svg)
The MAX232 is an
integrated circuit
An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
by
Maxim Integrated Products
Maxim Integrated, a subsidiary of Analog Devices, designs, manufactures, and sells analog and mixed-signal integrated circuits for the automotive, industrial, communications, consumer, and computing markets. Maxim's product portfolio includes po ...
, now a subsidiary of
Analog Devices
Analog Devices, Inc. (ADI), also known simply as Analog, is an American multinational semiconductor company specializing in data conversion, signal processing and power management technology, headquartered in Wilmington, Massachusetts.
The co ...
, that converts signals from a
TIA-232
In telecommunications, RS-232 or Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such a ...
(RS-232) serial port to signals suitable for use in
TTL
TTL may refer to:
Photography
* Through-the-lens metering, a camera feature
* Zenit TTL, an SLR film camera named for its TTL metering capability
Technology
* Time to live, a computer data lifespan-limiting mechanism
* Transistor–transistor lo ...
-compatible digital logic circuits. The MAX232 is a dual transmitter / dual receiver that typically is used to convert the RX, TX, CTS, RTS signals.
The drivers provide TIA-232 voltage level outputs (about ±7.5
volt
The volt (symbol: V) is the unit of electric potential, electric potential difference (voltage), and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta (1745–1827).
Defi ...
s) from a single 5-volt supply by on-chip
charge pump
A charge pump is a kind of DC-to-DC converter that uses capacitors for energetic charge storage to raise or lower voltage. Charge-pump circuits are capable of high efficiencies, sometimes as high as 90–95%, while being electrically simple c ...
s and external
capacitor
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of ...
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
TTL
TTL may refer to:
Photography
* Through-the-lens metering, a camera feature
* Zenit TTL, an SLR film camera named for its TTL metering capability
Technology
* Time to live, a computer data lifespan-limiting mechanism
* Transistor–transistor lo ...
levels.
These receivers have a typical threshold of 1.3 volts and a typical
hysteresis
Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of ...
of 0.5 volts.
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,
and MC1489 quad receiver chip required 5 volt power.
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 and designed by
Dave Bingham.
Maxim Integrated Products
Maxim Integrated, a subsidiary of Analog Devices, designs, manufactures, and sells analog and mixed-signal integrated circuits for the automotive, industrial, communications, consumer, and computing markets. Maxim's product portfolio includes po ...
announced the MAX232 no later than 1986.
Versions
The later MAX232A is
backward compatible
Backward compatibility (sometimes known as backwards compatibility) is a property of an operating system, product, or technology that allows for interoperability with an older legacy system, or with input designed for such a system, especially i ...
with the original MAX232 but may operate at higher
baud
In telecommunication and electronics, baud (; symbol: Bd) is a common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel.
It is the unit for symbol rate or modulatio ...
rates and can use smaller external capacitors 0.1
μF in place of the 1.0 μF capacitors used with the original device.
The newer MAX3232 and MAX3232E are also backwards compatible, but operates at a broader voltage range, from 3 to 5.5 V.
Pin-to-pin compatible versions from other manufacturers are ICL232, SP232, ST232, ADM232 and HIN232.
Texas Instruments
Texas Instruments Incorporated (TI) is an American technology company headquartered in Dallas, Texas, that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globall ...
makes compatible chips, using MAX232 as the part number.
Voltage levels
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.)
Applications
![RS-232 to TTL converters using MAX232](https://upload.wikimedia.org/wikipedia/commons/b/b5/RS-232_to_TTL_converters_using_MAX232.jpg)
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 and RS-485) and single-ended RS-232 albeit at reduced voltage.
References
External links
{{Wikibooks, Serial Programming, MAX232 Driver Receiver
MAX232 & MAX232A Maxim
Investigating Fake MAX3232 TTL-to-RS-232 Chips
Integrated circuits