Pos and Neg Logic

Wow! Bernie your not so out of touch as you imply. Positive logic refers to a 1 or true input to make a positive output. Negative logic refers to a 0 or false to make a positive output. In some logic systems they make a big point about this. In discrete logic "ie. TTL or CMOS integrated circuits or ICs'" it refers to the on or true state of the input. A high or 1 may "enable", a 0 or false may "enable", the circuit. With negative logic a zero or false input state would "enable" the logic and a 1 or true state would disable the logic.
Allot of stuff surrounds the XIC or XIO ladder commands in PLC products, as being positive or negative.
This has nothing to do with logic.
XIC means "exmamine if closed" and XIO means "examine if open".
Negative logic means to "Negate" the outcome based on positive input.

bitmore
 
Basically it's a "Logics 101" question. You can work with the 1s, what most people do, or you can make it hard on yourself and work with the 0s as schoolteachers like to do. And yes, some technology is based on negative logic, because of the design.

Kind regards,
 
A long time ago, I had a friend I worked with in circuitry design, but we were both stubborn. He did all of his core-logic in TTL (which is generally negative logic), and I did all of my interface and buffer logic in CMOS (which is generally positive).

Everything worked, but we could never just settle into one family.
 
Without talking about the voltage levels or the circuitry involved, you could say:

(positive)
X shall be THIS or THAT

(negative)
X shall not be not THIS and not THAT

fugly, isn't it?
 
I'm suprised no one mentioned that some logic views the glass as half full and some logic views it as half empty....

I think we need more students coming this way, some of you need some practice.... :D
 
Jeebs said:
I'm suprised no one mentioned that some logic views the glass as half full and some logic views it as half empty....

I think we need more students coming this way, some of you need some practice.... :D
Click to expand...

I'm an Engineer, I think your glass is too big....:p
 
jvdcande said:
Basically it's a "Logics 101" question. You can work with the 1s, what most people do, or you can make it hard on yourself and work with the 0s as schoolteachers like to do. And yes, some technology is based on negative logic, because of the design.

Kind regards,
Click to expand...

Thanks. so the one that us 1 as on is positive logic. and the one that uses 0 as on is negative logic? I was just wondering. i was looking at buying a plc system and they sell I/O some just pos and some just neg. some have both.
 

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