µP displays 10-bit data on three LED

-- EDN, November 7, 1996

Design Ideas

 µP displays 10-bit data on three LEDs

Yongping Xia, Philips Lighting Electronics, Torrance, CA

 The circuit in Figure 1

uses a PIC16C55 µP to read 10-bit binary data and directly display the data in decimal format on three common-cathode LED displays. If value of the data exceeds 999, the displays show three hyphens (---) to represent overflow. The PIC16C55 has high drive capability. Each output pin can source 20 mA and sink 25 mA; the outputs can thus directly drive the LED display.

  The output pins multiplex the display, turning only one digit on at a time for approximately 5 msec. The 10-bit data arrives on pins RA0 to RA3, RB0 to RB4, and RC0. The assembly program in Listing 1

arranges the input data, converts it to three BCD codes, converts each BCD word to a corresponding seven-segment code, and then routes the code to the output port. The clock for the µP runs at approximately 600 kHz with the components in Figure 1.
(DI #1937)

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