Hi,

The TX line is held HIGH from the master, through a 10K pull-up
resistor. The communication doesn't work *WITHOUT* the MAX232 connected.
It worked before, but not anymore. I have two connectors at the master
side, one for the slave, and one for the MAX232. Could it be that when
the MAX232 is not connected, some strange fields pull the line wrong ?
From my point of view, it should work fine without the connector for the
MAX232...
Should I remove the pull-up resistor from the master ? I guess this way
it could work with one slave, but not with more.


Lucian


-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Jan-Erik Soderholm
Sent: 23 august 2004 19:53
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: PIC Network Strange Behaviour

Lucian wrote :

> Here's a diagram of the configuration I have. In fact, I want the
> circuit to function without the MAX232 connected, but it
> doesn't. That's what I'm trying to figure out: why does now it only
> functions with the MAX232 connected to the line.

Hi !
(Refering to the attached GIF...)

I'd guess that when the PC is "idle", the MAX232 is holding
it's TX output *actively* high ("1"). That's why the slave can
not send data using it's own TX output. The slave and the
MAX232 will try to force that line in different directions.
If the MAX232 can source more current then the slave can drain,
the line will probably be kept in a high state.

What about a diod at the MAX232-TX, just as at the slave-TX ?

Jan-Erik.

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