How many 74LS low-power Schottky inputs can an output of MC9S12DG128 drive


I need to figure this out for a project and can't seem to find the answer. Does anyone know how I can figure this out? I think there is an equation to find this and can't seem to find the specification sheet for MC9S12DG128. What do I need to figure out about the MC9S12 to find the answer?

Best Answer

The MC9S12DG128 can sink or source an absolute maximum of 25mA from any GPIO pin (as stated in the datasheet).

The 74LS00 has \$I_{IH}\$ (in the example I found) of 20µA. It has an \$I_{IL}\$ of 0.4mA though, which is higher.

25mA / 0.4mA = 62.5.

So theoretically 62 74LS00 is the absolute maximum before you break the IO pin.