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How to use the MAX 3232 on my Professional Development Board? — Parallax Forums

How to use the MAX 3232 on my Professional Development Board?

SteveWoodroughSteveWoodrough Posts: 190
in Propeller 1
My apologies if this is a repeat subject. I have searched the forum and cannot locate the answer. How specifically does one use the Max 3232 E on my Prof Dev Board to interface with an rs232 device?

I am trying to interface with speed radar that transmits a constant length data string about twice a second. The signal is RS232 baud rate 9600 N81, and the communication voltages are +5 -5 Volts.

I’ve connected to the radar via Tera Term at 9600 baud and get a nominal device output of CD000000000000 . If the radar detects a 5 mph object, the output is CD005000000000 .

Now I want to “pump” this data from the radar rs232 into the prop and receive the data through the 4 port FDS object.

I plugged the radar output DB9 into the developers board DB9. Even though I know pin 2 (radar TX) has data on it ( I can see it with my scope), I get nothing on the Rx (3.3V) or the Tx (0v) from the 3232 output.

What step am I missing? How do I enable the MAX3232?

Than You,
Steve

Comments

  • LeonLeon Posts: 7,620
    The MAX3232 should just work if it is correctly connected, there is no enable pin.
  • Duane DegnDuane Degn Posts: 10,588
    You need to run a wire from the RX connector to one of the I/O pins on the Prop. You'll need to provide the serial driver with this I/O pin so it knows to watch for input on this pin.

    You'll probably want to start with a simple serial bridge and just output to the terminal whatever you receive as input.
  • Duane DegnDuane Degn Posts: 10,588
    Here's a link to a bridge program I wrote for a SayIt module. It would work with your device. You'll want to change the I/O pin constants to match your setup.
  • SteveWoodroughSteveWoodrough Posts: 190
    Null Modem.
    Thanks for the link Duane
  • JonnyMacJonnyMac Posts: 9,105
    edited 2016-06-05 04:07
    If the output of the device is 5V RS-232 you don't need the MAX chip -- just put a 10K resistor inline. You will probably have to use an inverted baud mode.
  • SteveWoodroughSteveWoodrough Posts: 190
    Jon,
    Thank you. Now that I am getting data via the 3232 I will experiment with the direct approach. I did see that you mentioned the resistor technique a few years back in a related rs232 post.
    Regards.
    Steve
  • LeonLeon Posts: 7,620
    What was the problem?
  • SteveWoodroughSteveWoodrough Posts: 190
    I did not have a null modem connection. Once I added a null modem adapter the 3232 worked correctly. For this gear head, anything beyond a blinking LED is a stretch.
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