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MAX232 question — Parallax Forums

MAX232 question

c.asmithc.asmith Posts: 15
edited 2014-01-18 09:23 in General Discussion
Hi, Guys,

I'm trying to interface a MAX232, but i'm unsure if I have the connections right, and i'm not getting any feedback from the serial device. Any recommendations would be grateful.

Cheers,

Cam.
MAX232.jpg
MAX232.jpg
1024 x 703 - 74K

Comments

  • Duane C. JohnsonDuane C. Johnson Posts: 955
    edited 2014-01-17 18:29
    I don't think it is connected up properly.
    See MAX232

    Duane J
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2014-01-17 18:31
    hmmm... it really is a bit of bad form to ask for Arduino support in this forum.

    In any event, can you disconnect the Ardunino and jury rig the Tx to Rx for a loopback test of the Max232. Whatever you typed from your terminal should show up on the screen if the Max232 is working right.

    It that is good, you will have to seek advice to what you are doing wrong with your Arduino (likely from elsewhere).

    You do seem to have one capacitor that you wired to pins and also short-circuited. And the Max232 has two pairs of Rx and Tx. It seems as if you have inputs on one pair and outputs on another. That won't work.
  • frank freedmanfrank freedman Posts: 1,983
    edited 2014-01-17 18:35
    you have C2 shorted on pins 4 and 5. pull up the max232 data sheet and lift that circuit as is.

    Frank
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2014-01-17 18:36
    Don't forget to connect Vss from the Arduino to the MAX232's Vss. Also your schematic shows a shorted cap, but you probably didn't mean it. And, as Duane says, you do not have the transmitters and receivers connected up correctly. For example, you have a connection to T2IN but not to T2OUT.

    -Phil
  • c.asmithc.asmith Posts: 15
    edited 2014-01-17 18:55
    Hi, Guys,

    I'm sorry about the Arduino stuff, but I also own SX processors and basic stamps :).

    I have the CP2 connected directly from PIN 4 to PIN 5. I couldn't draw it that well. But, on the breadboard its like this:

    PIN 4 -> Positive Capacitor pin -> Negative capicitor pin -> PIN 5
  • c.asmithc.asmith Posts: 15
    edited 2014-01-17 18:56
    I'm also not sure about how the capcitors should be placed in reference to Negative and positive for pins 2 and 6. Can someone break that down for me please.
  • TCTC Posts: 1,019
    edited 2014-01-17 19:05
    Check out page 17, figure 5 of this datasheet. It has the correct way to hook it up.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2014-01-17 22:08
    The Minus on the capacitor goes to the Minus on the chip, and the Plus goes to the Plus.

    Of course there are some capacitors that are not sensitive to polarity and then it doesn't matter. Usually if you put the polarized ones backwards, they blow up with a pop. But I think there is one capacitor on the MAX232 where polarity will work either way. I seem to remember something in the pdf fine print.

    Oh, a quick look at the pdf shows that PIN 6 capcitor has a Plus going to Ground and the Minus going to the Pin 6. That might throw you off, the Pin 6 is supposed to output -10 volts, so it is below Ground.
  • stamptrolstamptrol Posts: 1,731
    edited 2014-01-18 05:12
    Other details not withstanding, the connections for the data are wrong compared to the datasheet.

    pin 9 is ttl out for the corresponding rs232 in on pin 8

    pin 10 is ttl in for corresponding rs232 out on pin 7

    Cheers,
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2014-01-18 09:23
    Rx and the Tx are wrong? That is why the final proof is a physical loopback test without the Arduino. You don't waste a lot of time trying to find out what is wrong with your code when it isn't the code that is wrong.

    If you are going to build serial ports -- either RS232, RS422, RS485; do a physical loopback test before you hook up your microcontroller. It saves time and reduces headaches.
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