Explain code example - Raspberry Pi Forums

can explain going on in code example? bought kit sunfounder , terrible job of explaining project examples. book has wiring diagrams , code go along it. wrote code knowledge have, , did in 150+ lines of code, did in 50. it's shift register wired 7 segment display, , displays 0 - 9, - f in loop.

don't understand hexadecimal thing in hc595_shift(dat) , loop().

code: select all

#!/usr/bin/env python import rpi.gpio gpio import time  sdi   = 11 rclk  = 12 srclk = 13  segcode = [0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,0x7f,0x6f,0x77,0x7c,0x39,0x5e,0x79,0x71,0x80]  def print_msg():     print 'program running...'     print 'please press ctrl+c end program...'  def setup():     gpio.setmode(gpio.board)    #number gpios physical location     gpio.setup(sdi, gpio.out)     gpio.setup(rclk, gpio.out)     gpio.setup(srclk, gpio.out)     gpio.output(sdi, gpio.low)     gpio.output(rclk, gpio.low)     gpio.output(srclk, gpio.low)  def hc595_shift(dat):     bit in range(0, 8):         gpio.output(sdi, 0x80 & (dat << bit))         gpio.output(srclk, gpio.high)         time.sleep(0.001)         gpio.output(srclk, gpio.low)     gpio.output(rclk, gpio.high)     time.sleep(0.001)     gpio.output(rclk, gpio.low)  def loop():     while true:         in range(0, len(segcode)):             hc595_shift(segcode[i])             time.sleep(0.5)  def destroy():   #when program ending, function executed.     gpio.cleanup()  if __name__ == '__main__': #program starting here     print_msg()     setup()     try:         loop()     except keyboardinterrupt:         destroy() 

gpio.output(sdi, 0x80 & (dat << bit))

shift , mask operation. dealing here 8 bit byte. << operator performs shift dat shifted left bit times. if bit 7 bottom bit of dat shifted top. & operator performs bitwise and. if bit set in both operands set in result. 0x80 has top bit set result of 0x80&var non 0 of top bit in var set.

not sure why choose test top bit rather bottom iether work.

hope helps.

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