RS-232 Level Converter


This is a basic RS-232 transmit/receive circuit that is necessary for PIC microcontrollers to reliably communicate with a PC serial port. Why is it necessary? Well, the RS-232 specification requires that the signal levels be ±3-15 Volts and unfortunately the PIC microcontroller operates at TTL levels (0-5 Volts). The MAX233 is a nice IC that allows you to convert microcontroller voltages to RS-232 compatible levels with no required external components.

A MAX233 is used to convert the logic level signals of the PIC microcontroller to RS-232 compatible voltage levels. Technically the MAX233 is a RS-232 line driver/receiver, but an easier way to explain its operation is that it allows a PIC microcontroller to communicate at RS-232 voltage levels with a computer. The MAX233 should nominally be run at 5 Volts.


  1. Ricky
    // Reply


    Nice to browse this helpful website. Let me introduce myself, I am a newbie of scope project. And,I want to make a DIY USB scope with 2 Analog display and LCD display for personnel use. ^_^

    As the circuit of MAX 233 you posted, would you please advise which thing should “RS232-TRANSCEIVERP” connected. And, can I use the hardware connection just like Tinyloader mentioned. (MAX232, DB9 and PIC connected together)

    Thank you for your help.

  2. // Reply

    See pp. 21 of the MAX220-MAX249 datasheet ( for a good diagram of the necessary pin connections. The “RS232-TRANSCEIVERP” pins are the power pins of the MAX233. Eagle layout editor forces you to separate them from the IC package, which can make the schematic a little more confusing than it should be. You can use the Tiny Bootloader’s schematic too.

  3. The Arcade by Mioux Damned Blog » Archive du blog » Suite de mes aventures dans l’électronique
  4. Laurice
    // Reply

    what are specifically connected to ground in the DB9 connector? what do G1 and G2 represent?

  5. vlad
    // Reply

    this device programs my oscilloscope’s microcontroller while it is soldered in the circuit?

  6. hedi gharbi
    // Reply

    merci pour vous pour se projet .Elle me aidée beaucoup pour mon projet de fin étude.

  7. dan
    // Reply


    i would like to know the reason why max233 with rs232 is preferred over max232 with rs232

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