AVR-Chat

John Samperi wrote:
> At 05:52 AM 15/12/2005, you wrote:
> 
>>0/+3 happens to work on classic 1488/1489 buffers, "but its not right."
>>
>>Super serious workstations used to rigidly ahere to +-10 volts.
> 
> 
> 
> + - 25V being the 'right' voltage :-)
> 

The RS232 Standard specifies signals as between +-3V and +-25V.

Equipment must be able to withstand as much as +-25V and should be able 
to guarantee at least +-3V at the receiver. Consequently higher voltages 
than the minimum specified are used to overcome anticipated transmission 
line losses. +-10V is a convenient middling value.

Thus, nearly all of the above are 'right' in the sense that they are 
nominally compliant with the standard. Voltages in the range -3 < V < +3 
are forbidden and may generate indeterminate results. However the DS1489 
line receiver has a reverse diode to ground at the input and so anything 
less than about 1.25V will be detected as a low signal.

Pete Harrison