Overview

The MAX232 (MAX232N) is a dual RS-232 line driver and receiver IC manufactured by Texas Instruments and Maxim Integrated (Analog Devices). It converts 5V TTL/CMOS serial UART logic signals into true EIA/TIA-232-E (RS-232) bipolar voltage levels (±9V\pm 9\text{V}) and vice versa.

Equipped with an internal dual capacitive charge-pump voltage generator, the MAX232 generates +10V+10\text{V} and −10V-10\text{V} power rails internally using four external 1.0 μF1.0\ \mu\text{F} capacitors, operating completely from a single +5.0V DC power supply. It contains two independent transmitter channels (TTL to RS-232) and two receiver channels (RS-232 to TTL).

Quick reference

Supply Voltage (VCC)4.5 V to 5.5 V DC (+5.0 V nominal)
Data RateUp to 120 kbps120\text{ kbps}
Channels2 Drivers (TTL/CMOS to RS-232) & 2 Receivers (RS-232 to TTL/CMOS)
Charge Pump Capacitors4x 1.0 μF1.0\ \mu\text{F} electrolytic/ceramic capacitors (or 0.1µF for MAX232A)
RS-232 Output Voltage Level±9.0 V\pm 9.0\text{ V} typical
RS-232 Input Voltage Range±30.0 V\pm 30.0\text{ V} max
Package16-pin DIP / SOIC-16

Pinout (DIP-16 Package)

text
             ┌───┴───┐
        C1+ 1│ 1   16│ VCC (+5V)
        V+  2│       │15 GND
        C1- 3│       │14 T1OUT (RS-232 Level Out)
        C2+ 4│ MAX232│13 R1IN  (RS-232 Level In)
        C2- 5│       │12 R1OUT (TTL Level Out)
        V-  6│       │11 T1IN  (TTL Level In)
      T2OUT 7│       │10 T2IN  (TTL Level In)
       R2IN 8│       │9  R2OUT (TTL Level Out)
             └───────┘
PinNameTypeDescription
1C1+AnalogCharge pump 1 positive capacitor pin
2V+Analog Output+10V+10\text{V} charge pump output (Requires 1.0µF capacitor to GND)
3C1-AnalogCharge pump 1 negative capacitor pin
4C2+AnalogCharge pump 2 positive capacitor pin
5C2-AnalogCharge pump 2 negative capacitor pin
6V-Analog Output−10V-10\text{V} charge pump output (Requires 1.0µF capacitor to GND)
7T2OUTRS-232 OutTransmitter 2 Output (Connect to RS-232 DB9 Pin 2/3)
8R2INRS-232 InReceiver 2 Input (Connect to RS-232 DB9 Pin 3/2)
9R2OUTTTL OutReceiver 2 Output (Connect to MCU RXD)
10T2INTTL InTransmitter 2 Input (Connect to MCU TXD)
11T1INTTL InTransmitter 1 Input (Connect to MCU TXD)
12T1OUTRS-232 OutTransmitter 1 Output (Connect to RS-232 DB9 Pin 2/3)
13R1INRS-232 InReceiver 1 Input (Connect to RS-232 DB9 Pin 3/2)
14R1OUTTTL OutReceiver 1 Output (Connect to MCU RXD)
15GNDGroundGround reference (0 V)
16VCCPowerPositive supply input (+5.0 V DC)

Wiring (Single MCU UART Channel to RS-232 DB9 Connector)

text
  Charge Pump Capacitors Setup:
  - C1: 1.0µF between Pin 1 (C1+) & Pin 3 (C1-)
  - C2: 1.0µF between Pin 4 (C2+) & Pin 5 (C2-)
  - C3: 1.0µF between Pin 2 (V+)  & VCC (+5V)
  - C4: 1.0µF between Pin 6 (V-)  & GND

  Microcontroller 5V UART              MAX232                 DB9 Male RS-232 Connector
  ┌───────────────────┐        ┌───────────────────┐        ┌─────────────────────────┐
  │   MCU TXD         ├───────►│ Pin 11: T1IN      │        │                         │
  │                   │        │ Pin 14: T1OUT     ├───────►│ Pin 2: RXD (RS-232)     │
  │   MCU RXD         │◄───────┤ Pin 12: R1OUT     │        │                         │
  │                   │        │ Pin 13: R1IN      │◄───────┤ Pin 3: TXD (RS-232)     │
  │   GND             ├───────►│ Pin 15: GND       ├───────►│ Pin 5: GND              │
  └───────────────────┘        └───────────────────┘        └─────────────────────────┘

Common mistakes

  • Reversing polarity of charge pump capacitors: Electrolytic capacitors on V+V+ (Pin 2) and V−V- (Pin 6) must have correct polarity: Pin 2 positive to VCCVCC; Pin 6 negative to GND.
  • Connecting MAX232 directly to 3.3V MCUs: The original MAX232 requires VCC=5.0VVCC = 5.0\text{V} and outputs 5V TTL logic levels on R1OUT/R2OUT. When interfacing with a 3.3V microcontroller (such as ESP32 or STM32), use the 3.3V-native MAX3232 IC instead.

Notes

  • MAX232 vs MAX3232: MAX232 operates on 5.0V only and requires 1.0µF capacitors; MAX3232 operates on 3.0V to 5.5V and uses smaller 0.1µF capacitors.

Assets & downloads