MAX232

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#1
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Hi all,
I'm trying to use the USART interface of my atxmega256a3: I've attached it to a PL2303 and I can see data going through the wire, but bytes are mapped into different octets.
Is this due to the missing MAX232 levels converter?
What if I used an FTDI FT232xx where

1) xx=BL
2) xx=RL

Would I still need the MAX232 in the middle?

Thanks a lot in advance for the support.
RM

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The PL2303 is a USB to RS-232 converter.

You need to convert the 3.3 V logic level from the Xmega USART to RS-232, then tie that to the RS-232 to USB converter.

The RS-232 level converter also inverts the signal, so you are missing an inversion in your signal chain, unless you are using an inverted signal driver for your Xmega.

It technically is possible for some RS-232 devices to respond to logic level signals, but this is OUT OF SPEC, and regardless, if doing so you would need to invert the signal.

MAX232, by the way, is for a 5V level serial communications signal. Max3232, (IIRC), is for a 3V logic level signal to RS-232 level.

JC

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DocJC wrote:
The PL2303 is a USB to RS-232 converter.

You need to convert the 3.3 V logic level from the Xmega USART to RS-232, then tie that to the RS-232 to USB converter.

The RS-232 level converter also inverts the signal, so you are missing an inversion in your signal chain, unless you are using an inverted signal driver for your Xmega.

It technically is possible for some RS-232 devices to respond to logic level signals, but this is OUT OF SPEC, and regardless, if doing so you would need to invert the signal.

MAX232, by the way, is for a 5V level serial communications signal. Max3232, (IIRC), is for a 3V logic level signal to RS-232 level.

JC

Ok, I *think* I'm getting it. Therefore the FDTI would be suitable as is, without max.. as it accepts UART signal levels.

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Yes.

JC

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DocJC wrote:
Yes.

JC


Thanks a lot

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DocJC wrote:
The PL2303 is a USB to RS-232 converter.

You need to convert the 3.3 V logic level from the Xmega USART to RS-232, then tie that to the RS-232 to USB converter.


Have you ever read a PL2303 datasheet?

Warning: Grumpy Old Chuff. Reading this post may severely damage your mental health.

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If you are talking about the PL2303 chip itself, it has logic level outputs (selectable 3.3v/5v levels, active hi). It can be connected straight to the xmega without anything in the middle. If you are talking about an adapter that uses the PL2303 chip and has a DE9 connector on it (apparently also called PL2303 by some), it would need level shifter (MAX3232) between it and the xmega.

FTDI is a different company that also makes both USB-serial chips and USB-RS232 adapters. Likewise, the chip or logic-level adapter cables can connect straight to the xmega; the adapters with DE8 connectors would need level shifters.

/mike

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RM did not include a link for his particular PL2303. When I Googled it, I found a USB to RS-232 Adapter, hence my advise above.

Obviously a different approach is called for if one uses the chip instead of the cable.

As a FTDI user, the PLxxx kind of rang a bell, but not enough for me to recognize it...

JC