inputs for the microcontroller

[evaradharaj]

Hi,
How many outputs can we take from one pin of the microcontroller that will not affect the normal operation of the microcontroller?
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[SherpaDoug]

To see how many inputs the output of a PIC can drive:

1) Find in the PIC datasheet under "Electrical Characteristics" the maximum current you can get from a pin (usually 25mA). If you are using more than 1 pin in a port also find the max current for the port (usually 50ma).

2) Next find in the datasheet the graph of voltage vs current, with a name like "TYPICAL, MINIMUM AND MAXIMUM VOH vs. IOH (VDD = 3V, -40°C TO +125°C)".

3) For all your loads find the voltage they need to operate and the current they draw at that voltage.

4) Add up the currents the loads draw at the highest load's voltage.

5) Make sure that current is below the pin and port limits.

6) Make sure from the graph that the PIC will supply enough voltage at that current.

7) If high speed is important you must add up the capacitance of the loads, and an estimate of the wiring capacitance. Use T=RC to estimate the time delay that capacitance will cause.
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[dyeatman]

He might also want to make sure his power supply can handle the additional load without sagging or spiking...
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