TTL to/from RS232 Signal Conversion

NEW! RLC-2 RS232 Level Converter in a DB9 backshell

Paul B. Webster says:

Technically, there is *no* RS-232 standard showing [how data bits are related to signal levels], and never will be because RS-232 is a level-zero = "physical" level standard. It defines wires, voltages and pins. What travels on that layer, the level-one or "transport" layer, is something else again.

Methods

• TTL to RS232
• RS232 to TTL

Most RS232-TTL conversion is done with a IT/Maxim MAX232^, MAX3232^ or similar chip.

Peter L. Perez says:

[For an RS232 PIC interface] you don't need diodes, you need a 10K resistor for the incoming data (towards the chip) and a 220 ohm on the outgoing (from the chip). If your application is low current or sleeps you also need a zener or other clamping device across the micro power supply. I certify that this works up to 9600 Bauds at least ;-). You can use the same pin for Tx and Rx and save a resistor ;-) I can also certify that certain renowned PLL chips and other I2C peripherals do not like the -0.6V appearing on the input pin at all, and behave strangely, so your mileage will vary. Again: PICs will work like this, but other micros may not.

PS: If you reduce the input resistor from 10k to ~3k3 then it can also power the PIC temporarily (hint: set break state on RS232 and wait for filter cap across PIC power pins to charge...). You HAVE to use a clamping device for this. 5V6 Zener (0.25W low leakage) will do fine.

See also:

• http://www.romanblack.com/bitbangserial.htm Roman Black shows how to connect a PIC 18F1320 to a PC serial port with just two resistors and some big banged c code. Then he goes on to connect a Sharp GP2 infrared distance sensor which provides accurate readings from 10 to 80cm.+
• http://www.tronisoft.com/4210.php Tronisoft has a new kit version of the RS232 to TTL converter
  +
• megamanv at spamgmail.com refers to

  http://www.botkin.org/dale/rs232_interface.htm http://www.botkin.org/dale/rs232_interface.htm
  
  Look no further. This simple design is no joke. With only two npn mosfets (they don't even have to match!) and two 2k-20k resistors, you can have you're very own self adjusting level independent rs232 interface. It works and its so simple that you can memorize it! Get it now before the link disappears!

  http://www.botkin.org/dale/rs232_interface.htm This can be done SO much more simply. Don't get hung up on bipolar transistors; this is a switching job, thre are better tools. Use two small MOSFETs and two resistors and do it the easy way! +
   

• http://www.embedinc.com/products/ser/index.htm +
• http://www.al-williams.com/awce/rs1.htm You can find a MAX232 board/kit designed to work with a breadboard here...
• http://www.digitalnemesis.com/catalogue/ Sells a RS232 to 5-Volt level converter in a DB-9 backshell. Plugs into any 0.1" header to connect to your circuit.
• http://www.maxim-ic.com/ MAX232 TTL to/from RS232 level converter.
• http://www.edtn.com/embapps/e043fg2b.htm Bitscope RS-232 interface section
• http://www.national.com/an/AN/AN-681.pdf Nationals app note for a mouse

RS-232@

Ubicom demo modem board

James Michael Newton says:

http://www.dontronics.com/dt207.html A SimmStick with most of what users need, plus a little power supply section to run it all. People buy them just for the TTL/RS-232 conversion to D-9 connector, which makes it very simple.

Archive:

• PICList post "OptoIsolated PIC<>RS232 Interface" +

Comments:

• TTL to RS232 module with buit in PSU available in UK+

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