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always +2V on my RC7/RX Pin???

 
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YulL



Joined: 29 Sep 2004
Posts: 39
Location: Paris (France)

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always +2V on my RC7/RX Pin???
PostPosted: Wed Sep 29, 2004 9:03 am     Reply with quote
Is it normal : +2V on RC7 with PIC16F873???
...
Embarassed
It is connected to my MAX232 on the R2out Pin (9)
Ttelmah
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Re: always +2V on my RC7/RX Pin???
PostPosted: Wed Sep 29, 2004 9:22 am     Reply with quote
YulL wrote:
Is it normal : +2V on RC7 with PIC16F873???
...
Embarassed
It is connected to my MAX232 on the R2out Pin (9)

Simple answer.
No.

This input is a Schmitt input, so requires to be driven to 0.8*Vdd, to be seen as 'on'. The Max232, normally happily does this. Disconnect the pin from the track (if the chip is socketted, bend it out), and verify the voltage on the pin, and on the socket. It sounds as if something else is shorting the pin, preventing it being pulled properly up, or as if your software is not configuring the pin properly, and it is trying to operate as an output, or that the MAX232, is not receiving it's 5v supply.

Best Wishes
asmallri



Joined: 12 Aug 2004
Posts: 1635
Location: Perth, Australia

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PostPosted: Wed Sep 29, 2004 9:28 am     Reply with quote
The PC received data from the PIC so the problem will not be the 5 volt supply. It is most likely two outputs driving in opposite directions
Ttelmah
Guest
PostPosted: Wed Sep 29, 2004 10:29 am     Reply with quote
asmallri wrote:
The PC received data from the PIC so the problem will not be the 5 volt supply. It is most likely two outputs driving in opposite directions

Don't be quite so sure about this. :-)
I have seen exactly this behaviour, when a designer had connected the MAX232, to 3.3v, instead of 5v, it ran for transmit, but gave a very low receive voltage. This is why I suggested the possibility...
However I see in another thread, that the poster has traced it to incorrect wiring round the MAX232 itself.

Best Wishes
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