AVR-Chat

On Dec 14, 2005, at 3:36 PM, 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 specified range is 3 to 30, positive and negative, with -3 to +3  
being the "keep out zone".

+-5 and +-12 used to be very common voltages to have inside a  
computer as Once Upon A Time common DRAM memory required negative  
voltage bias to operate.

The 1488 driver dropped about 2 volts so when driven with +-12 its  
output would swing +-10.

+-25 was much harder to drive a clean signal any interesting distance  
so the RS-232 spec is limited to 19,200 and 50'. Lower voltages work  
longer distances and higher data rates which prompted the move to LVD  
drivers.

--
David Kelly N4HHE, dkelly@HiWAAY.net
========================================================================
Whom computers would destroy, they must first drive mad.