RS-232 Level Converter

January 31, 2006

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
    November 26, 2006 at 5:40 AM | #1

    Hello,Steve,

    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. November 27, 2006 at 1:30 PM | #2

    See pp. 21 of the MAX220-MAX249 datasheet (http://datasheets.maxim-ic.com/en/ds/MAX220-MAX249.pdf) 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. May 19, 2008 at 10:52 AM | #3

    BTW – you can get ready made or kit versions of the RS-232 to TTL Level Converters from:

    Hope that helps.

    http://www.tronisoft.com

  4. d
    June 6, 2008 at 2:38 AM | #4

    thanks you have been very very help full

  5. ibraheem
    November 1, 2008 at 7:59 AM | #5

    i ask if there is a usb level converter

  6. Laurice
    January 8, 2009 at 10:22 PM | #6

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

  7. vlad
    September 5, 2009 at 10:27 AM | #7

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

  8. hedi gharbi
    June 4, 2010 at 1:49 PM | #8

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

  9. June 27, 2011 at 10:51 AM | #9

    Can u explain more about RS232 specification and microcontroller relation to it.

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