On 21-Jan-02 Tony Pan wrote:
> Thank you for the reply!
>
> Is TTL input the "regular" input that does not have the noise elimination
> feature?

Ok, here's a simple explanation....

The label "TTL input" is to do with the signal levels used to represent
'0' and '1'.   Look at the specs for Vil and Vih and you will see that it
essentially means that voltages near 0v are '0's and voltages near +5v are
'1's.  There is a region between these levels where the input is undefined

The label "schmitt trigger" can be applied to TLL and non-TTL compatible
inputs.

The definitions of '0' and '1' are similar for schmitt and non-schmitt TTL
inputs, but the points at which the change from '0' to '1' (and '1' to '0')
are different.  For regular input the decision points for '0' to '1' and for '1'
to '0' are the same.  For a schmitt trigger the '0' to '1' decision happens at
a higher voltage than the '1' to '0' decision.


I hope this helps.

>
> Tony
>
> P.S. I did find  a software bug. I accidentally set port D in parallel slave
> port mode.

I suspected as much but since I've not looked at that PIC I wasn't sure exactly
what port D supported.

Peter.

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu