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Topic: ATMEGA328 and PL2303HX (Read 3321 times) previous topic - next topic


Can I connect the Serial ports of the PL2303HX to the ATMEGA328, as I read online, the tolerance level of the serial port signal of the PL2303HX are 2-3.3v but the ATMEGA328 tolerance is 5v.

Should I hook up a voltage divider between the TX of the ATMEGA328 and the RX of the PL2303? or would the PL2303HX can tolerate 5v?



As far as I understand by reading the data sheet, the RS-232 input lines are 5 volt tolerant. Apparently the chip has a pin (4) called  vdd_232 which you can use to set the voltage of output-lines, which would protect connected MCU's tolerating 3-3.3V max. So, yes, it should be possible.

"RS-232 VDD. The RS-232 output signals (Pin 1 ~ Pin3) are designed for 5V, 3.3V or 3V
operation. VDD_232 should be connected to the same power level of the RS-232 interface. (The RS-232
input signals are always 5V~3V tolerant.) Note: This document version only provides 5V DC characteristic information. Refer to future revisions for updates.  (Document Revision: 1.6
Document Release: April 26, 2005) "


Mar 10, 2013, 02:03 pm Last Edit: Mar 10, 2013, 02:07 pm by n0idea Reason: 1
I guess you were reading the datasheet of the PL2303 not the PL2303HX because in the datasheet of the PL2303HX it is stated that pin 4 VDD325:

RS232 VDD. The power pins for the serial port signals . When the serial port is 3.3V, this should be 3.3V. When the serial port is 2.5V, this should be 2.5V


You can check it out for comparison and there's also a schematic at the end, I just want to know if it'll work with 5v directly.


In the datasheet it is stated for the RX pin "SCHMITT In, 5V Tolerant, Input Pad. Level and Driving Capability decided by VDD_325.'

So basically if i powered pin 4 VDD_325 with 5v it should work fine.


You're right, I shouldn't trust googles results that fast, after looking it up once it indeed was the wrong datasheet, sorry.

It's nice those input pins indeed are 5 volt tolerant, but.... I wonder how 5v-tolerant the vdd325-pin is.
The HX-less version can take 5volt, but the selectable vdd325 voltage of the HX is 1.8-3.3v, applying 5 volts may be too much.
An input pin on arduino will see anything below 0.5 volts as low and above ~2 volts as high though, it doesn't need 5v. I'd apply 3.3 volt to the vdd325 pin to stay within limits, with a good chance that it will work.

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