Файл: Microcontroller Programming. Thi Micro Chip PIC (Julio Sanchez, 2007).pdf

The circuit in Figure 10-5 can be programmed to do different functions. For example, the eight LEDs can be visualized as representing an 8-bit binary number and the circuit can be programmed to count in binary from 0 to 255. Since the eight LEDs are all wired to Port-B, the binary count can be directly echoed on the port. The following program, named LEDCount, performs this operation:

;File: LEDCount.asm

;Date: June 3, 2006

;Author: Julio Sanchez

;Processor: 16F84A

;Description:

;Circuit with eight LEDs wired to RB0 to RB7.

;Program displays a binary count from 0 to 255 on

;LEDs.

;===========================

;switches ;===========================

;Switches used in __config directive:

;_PWRTE_OFF

;|

;|_____ * indicates setup values processor 16f84A

include <p16f84A.inc>

__config _XT_OSC & _WDT_OFF & _PWRTE_ON & _CP_OFF

;=====================================================

; variables in PIC RAM

;===================================================== ; Declare variables at 2 memory locations

;========================================================

; m a i n p r o g r a m

;========================================================

;============================= ; space for interrupt handler ;=============================

org 0x04 ;=============================

;main program ;============================= main:

;Initialize all lines in Port-B for output

end

10.3 Programming the Seven-segment LED

A 7-segment display can be connected to output ports on the PIC and used to display numbers and some digits. The circuit in Figure 10-6 shows one possible wiring scheme.

As the name indicates, the seven-segment display has seven linear LEDs that allow forming all the decimal and hex digits and some symbols and letters. Once the mapping of the individual bars of the display to the PIC ports has been established, digits and letters are shown by selecting which port lines are set and which are not. For example, in the seven-segment LED of Figure 10-5, the digit 2 is displayed by setting segments a, b, g, e, and d. In this particular wiring, these segments correspond to Port-B lines 0, 1, 6, 4, and 5.