MAY ? They are also characterized for use as buffers for driving TTL inputs. These circuits are compatible with most TTL families. Inputs are diode-clamped to minimize transmission-line effects, which simplifies design. Typical power dissipation is mW, and average propagation delay time is 12 ns. N SOIC?
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There are two general types of outputs in digital circuitry: push-pull and open-collector OC. Push-pull outputs, which are in the 74LS04 drive the output high to the level of the power input of the chip, typically 5v or 3. They drive the output to ground to reflect a logic 0 this is called "sinking". What good is that? One example is several devices with interrupt outputs feeding into a single interrupt pin on a microcontroller. When there is no interrupt, the line is high. How, if no output is driving it high?
Somewhere there will be a "pull-up resistor" common values are 4. Then when an interrupt occurs, the chip causing the interrupt will pull the line to ground. Since the pull-up resistor is a fairly high value, this will not draw very much current, about 1 mA for a 4.
The line into the microcontroller going to a logic 0 will be recognized as an interrupt -- since this is caused by the line going from high to low, this is called an "active low" signal. Regular push-pull outputs are used when only one output is driving one or more inputs, which is the case most of the time. The 74LS05 is probably more expensive because there is much less demand for the chip.
74LS07 - 74LS07 Hex Buffer/Driver (Open Collector)