Any Cmos device is likely to draw a lot of current if it's inputs are left floating. Try tying the inputs to ground with 10K resistors and see if the current is the same from the data sheet at least pins 1 thru 7 and use the same resistor and tie them high as they are marked active low on the data sheet Also I'd put a .1uF bypass cap directly on that part... There's a lot of transistors in that package and the inputs are fairly high resistance as it is an LS (Low Power Schottky) part. The originals were TTL compatible and as fast as Cmos at the time they were introduced. Since they were pin for pin replaceable with regular TTL or Schottky logic and drew about 10 - 20% of the other non cmos logic families, they caught on for lower speed applications. The data sheet indicates differently but it was my experience when I actively worked with TTL logic that the LS family was slower than the TTL counterparts. Have you ever tried Eprom logic?... It was a cheap method to interface a 7 or 15 Segment LED to a computer it takes an eprom and an 8 bit latch for each display I used to drive some of the led displays directly from the latch's. Eprom logic was at that time just a step or so out of line with PLa's or PLD's. (I talk too much)
Bob
74LS181.pdf (159 KB)