MAX3221: No transmit or recieve on loopback test

Michael Majdalani

Part Number: MAX3221

Hi,

I am trying to establish serial communication from an Odroid-C2 MCU to a Host PC using the MAX3221. I have attached an image of my schematic. I am doing a loopback test where I have RX and TX connected on the Odroid side (Txin and Rxout) but am not recieving any data after sending.

V+ and V- are both at approximately 5.55V so the chip is on.

Is there any advice to test? When connected to host-pc I could not establish communication either.

Thanks

over 5 years ago

0 Hao L over 5 years ago

TI__Mastermind 25705 points

Michael,

Before we debug the loopback function, let's make sure the device work normally. Your schematic looks good to me. However could you confirm V+/V- voltage? RS-232 has +15V to -15V signaling. V+ and V- are charge pump output of MAX3221, which governs the driver output amplitude. V+ and V- of MAX3221 are around 5.4V and -5.4V in normal operation. You could check it with a scope or a multimeter. Here is an app note about charge pump with some waveforms for your reference.

e2e.ti.com/.../how-the-rs-232-transceiver-s-regulated-charge-pump-circuitry-works

Regards,

Hao

0 Michael Majdalani over 5 years ago in reply to Hao L

Prodigy 50 points

Hi Hao,

Sorry, I forgot I had posted this. The problem was solved by replacing the chip, it is possible there was a bad solder joint. Everything is working as intended.

Thank you!

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MAX3221: No transmit or recieve on loopback test