Scanning 7-Segment

Since the output buffer of P1 can sink 20mA (each output pin, but maximum IOL for all outputs was limited at 80mA), thus we can use P1 to drive LED display directly. As shown in the circuit, Two common-anode 7-segment LEDs are connected to P1 with 180 Ohms current limiting resistor. Each segment of two LED are tied in parallel to P1. Q1 and Q2 are activated by logic low of P3.0 and P3.1, sourcing +5V to common anode pins. P3.4 read logic low if either S1 or S2 was pressed while scanning period have made.



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7-SEG.C