Digilent 410-044-10P-KIT Manual de usuario descargar pdf (Pagina 17)

Spartan-3 Starter Kit Board User Guide www.xilinx.com 17

UG130 (v1.1) May 13, 2005 1-800-255-7778

The LED control signals are time-multiplexed to display data on all four characters, as

shown in Figure 3-2. Present the value to be displayed on the segment control inputs and

select the specified character by driving the associated anode control signal Low. Through

persistence of vision, the human brain perceives that all four characters appear

simultaneously, similar to the way the brain perceives a TV display.

This “scanning” technique reduces the number of I/O pins required for the four

characters. If an FPGA pin were dedicated for each individual segment, then 32 pins are

required to drive four 7-segment LED characters. The scanning technique reduces the

required I/O down to 12 pins. The drawback to this approach is that the FPGA logic must

continuously scan data out to the displays—a small price to save 20 additional I/O pins.

Figure 3-2:

Drive Anode Input Low to Light an Individual Character

AN3

AN2

AN1

AN0

DISP3 DISP2 DISP1 DISP0

{A,B,C,D,E,F,G,DP}

UG130_c3_02_042404

1 2 ... 12 13 14 15 16 17 18 19 20 21 22 ... 63 64

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Digilent 410-044-10P-KIT Manual de usuario Pagina 17