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.

23 Comments / Add your own comment below

  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. 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.

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

    Hope that helps.

  5. thanks you have been very very help full

  6. i ask if there is a usb level converter

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

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

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

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

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  23. hello

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

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