shift register all outputs high

i using 74hc595n 7 segment display. code me identify bits controlling specific segments, reason when last segment displayed, light up. byte sent register has value of 128 , yet acts 255. more bizarre same thing values on 128. also, expected, 127 shows last segment.

here's code:

code: [select]


const int datapin1 = 4;    //pin 14 on chip
const int latchpin = 5;    //pin 12 on chip
const int clockpin = 6;    //pin 11 on chip

int incomingbyte;
int i=0;

byte onesdigit = 0;

void setup()
{
  serial.begin(9600);
  pinmode(datapin1,output);
  pinmode(datapin2,output);
  pinmode(latchpin,output);
  pinmode(clockpin,output);
  onesdigit=0;
  serial.println("would iteration?");
}

void loop()
{
  updateregister1();
 
  if(serial.available())
  {
    incomingbyte = serial.read();
  }
 
  if (incomingbyte==121)
  {
    onesdigit=0;
    bitset(tensdigit,i);
    updateregister1();
    serial.print("i value: ");
    serial.println(i);
    i++;
    serial.print("onesdigit value: ");
    serial.println(tensdigit);
   
    serial.println("would iteration?");
  }
  incomingbyte=1;
 
  if(i>8)
  {
    i=0;
  }
   
}


void updateregister1()
{
  digitalwrite(latchpin, low);
  shiftout(datapin1, clockpin, msbfirst, onesdigit);
  digitalwrite(latchpin, high);
}


i have no idea problem is. advice?

supply decoupling on shift register. have got any?
http://www.thebox.myzen.co.uk/tutorial/de-coupling.html

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