sn74ls86n IC output voltage lower than 5v

[Elyxircuit]

When using a sn74ls86n IC (powering it correctly) when I input 5v to input 1A, and ground to input 1B I measure output 1Y as 3-4v. Can anyone help explain why the output is not 5v?

[retiredfeline]

Shhh, no need to shout.

Because it's has a TTL output stage with totem-pole transistor configuration so it doesn't go all the way to 5V. In 5V TTL, logic 1 is defined as > 2.4V.

See the typical output schematic in this article: https://en.wikipedia.org/wiki/Transistor%E2%80%93transistor_logic

[Elyxircuit]

If logic 1 is > 2.4V, then if one of the inputs to the ic is > 2.4v then will it still count as a logic 1 to the ic?

[TimFox]

Two important specs for any digital gate:
V_IHmin is the minimum input voltage that is guaranteed to be recognized as logic 1.
V_OHmin is the minimum output voltage that is produced for logic 1.
Obviously, for this to work reliably, V_OH > V_IH
Look at the data sheet for these values and the conditions under which they are specified (such as input current, etc.)
For most CMOS familes, V_OHmin is close to the positive supply voltage, but for TTL the guaranteed output is considerably lower.

[CaptDon]

I guess you don't work with 74XX I.C.'s much, even the spec sheet says it won't go to +5vdc. Look at those nifty things called datasheets.
Turn off the CAPS, you know better......Unless you are using an ancient 1940's teletype machine for your terminal, then you may not have a choice.

[TimFox]

By the way, if you need to drive a CMOS input from a TTL output, both on +5V supply, a resistor from the TTL output to +5V (roughly 10 k) will pull up the voltage higher to match the somewhat higher input voltage requirement of the CMOS input.  This is a quantitative question, so look at the data sheets to determine voltage requirements and current capability of the output.