----- Original Message ----- 
From: "apptech" <apptech@paradise.net.nz>
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Sent: Sunday, January 25, 2009 01:12
Subject: Re: [PIC] Do I need a transceiver?


>> Basically, Olin is suggesting that you take two Schottky diodes (D1 and
>> D2),
>> and:
>>
>>    - Connect anode of D1 to the signal line, and cathode to Vcc
>>    - Connect cathode of D2 to the signal line, and anode to Gnd
>>
>> What this will do, is protect the Rx input by keeping the voltage on the
>> signal line from going above Vcc, and below Gnd.
>
> ... by more than a Schottky diode drop in each case.

I knew somebody would bring this up, but decided to leave this bit of 
information out for the sake of brevity. >:)


 > In practice this violates the spec sheet requirements in SOME cases and 
not
> others BUT works OK in *almost* every case.
>
> YMMV but usually won't.

And when it will, you probably won't know for sure it was the Schottkys.


> Note that the current able to flow through the series resistor must be 
> less
> that the supply current if the supply rail is not to be "pumped up" by ths
> system. This is almost never a problem, but has causght some people out in
> special situations.

Brrrr... come again?

Vitaliy 

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