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RTS CTS Problem

Hi all ,

I am using GPIO lines of an AVR to control the RTS & CTS lines of the RS232 interface. The level convertor that I am using is MAX3222.

Software wise when the AVR is configured as a DCE so the RTS line is input and CTS is output , the software sets the GPIO going to the CTS high as long as it has buffer space , when it is wants the DTE to stop sending data it pull the GPIO low.

the problem is that when I set the CTS AVR GPIO high(1) the voltage that I see the 9 way connector pin is -5v and when I set CTS AVR GPIO to low(0) the voltage on the 9 way connector is 0v.

Is that the expected behavior? I think i am missing some fundamental concept.

BR rate

Reply to
ratemonotonic
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A low into the MAX should give you a positive voltage and a high a negative voltage. There should never be a 0V ever. It is not defined.

Reply to
James Beck

It is the expected behaviour allright if the buffers you use are inverting (they normally are). But you need to drive CTS _low_ to enable data flow, not high. This is how all CTS inputs (past buffers, at TTL level) I have seen work. :-)

Dimiter

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Reply to
Didi

By _low_ do you mean 0 on the AVR GPIO, sorry just clarifying. When will RS232 be banned? :- {)

Reply to
ratemonotonic

Yes.

Hah, it is that more or less is already - try to buy a laptop with it. :-)

It is still pretty useful for lowest level debugging etc., at the very begining of projects or when not all of the stuff is functional.

Dimiter

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IO

Reply to
Didi

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Fixed the problem , faulty IC (MAX322). was not raising the voltage up when GPIO was going low. thanks for clearing my this out.

BR rate

Reply to
ratemonotonic

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