Stepper motor problems

Eric Therriault

I recently got stepper motors from parallax to use in my project. It involves outputting to the parallel port and using that to drive the motor.
setup is as follows:
computer->parallel port->ULN2803A->stepper motor

I am using visual studio c# 2008 to code it (for project reasons), and my stepping works perfectly for full stepping (normal and high torque).
The problem that I am having is when I do Half Stepping, the first step is very small, maybe a 1/8 step, then the 2nd step will be 7/8 step, so although every 2 steps is = to a full step, the individual steps are not half steps, to ease this i will post my code so far.

[color=#0000ff]private[/color] [color=#0000ff]void[/color][color=#000000] btnhalfstep_Click([/color][color=#0000ff]object[/color][color=#000000] sender, [/color][color=#2b91af]EventArgs[/color][color=#000000] e)[/color]
{
   stopnow();//stops any other stepping being done
   interval = [color=#2b91af]Int32[/color].Parse(maskedtxtinterval2.Text);
   halfsteptimer.Interval = interval;
   halfsteptimer.Tick += [color=#0000ff]new[/color] [color=#2b91af]EventHandler[/color](half_step);
   halfsteptimer.Enabled = [color=#0000ff]true[/color];
}

[color=#0000ff]void[/color][color=#000000] half_step([/color][color=#0000ff]object[/color][color=#000000] o1, [/color][color=#2b91af]EventArgs[/color][color=#000000] e1) [/color][color=#008000]//Makes the leds counting in binary form[/color]
{
[color=#0000ff]if[/color] (rdclockwise.Checked == [color=#0000ff]true[/color])
{
[color=#0000ff]if[/color] (halfstep < 8)
{
[color=#0000ff]switch[/color] (halfstep)
{
[color=#0000ff]case[/color] 0:
[color=#2b91af]PortAccess[/color].Output(address, 1);
[color=#0000ff]break[/color];
[color=#0000ff]case[/color] 1:
[color=#2b91af]PortAccess[/color].Output(address, 3);
[color=#0000ff]break[/color];
[color=#0000ff]case[/color] 2:
[color=#2b91af]PortAccess[/color].Output(address, 2);
[color=#0000ff]break[/color];
[color=#0000ff]case[/color] 3:
[color=#2b91af]PortAccess[/color].Output(address, 6);
[color=#0000ff]break[/color];
[color=#0000ff]case[/color] 4:
[color=#2b91af]PortAccess[/color].Output(address, 4);
[color=#0000ff]break[/color];
[color=#0000ff]case[/color] 5:
[color=#2b91af]PortAccess[/color].Output(address, 12);
[color=#0000ff]break[/color];
[color=#0000ff]case[/color] 6:
[color=#2b91af]PortAccess[/color].Output(address, 8);
[color=#0000ff]break[/color];
[color=#0000ff]case[/color] 7:
[color=#2b91af]PortAccess[/color].Output(address, 9);
[color=#0000ff]break[/color];
}
}
halfstep += 1;
[color=#0000ff]if[/color] (halfstep == 8)
{
halfstep = 0;
}
}
[color=#0000ff]if[/color] (rdcounterclockwise.Checked == [color=#0000ff]true[/color])
{
[color=#0000ff]if[/color] (halfstep < 8)
{
[color=#0000ff]switch[/color] (halfstep)
{
[color=#0000ff]case[/color] 0:
[color=#2b91af]PortAccess[/color].Output(address, 1);
[color=#0000ff]break[/color];
[color=#0000ff]case[/color] 1:
[color=#2b91af]PortAccess[/color].Output(address, 9);
[color=#0000ff]break[/color];
[color=#0000ff]case[/color] 2:
[color=#2b91af]PortAccess[/color].Output(address, 8);
[color=#0000ff]break[/color];
[color=#0000ff]case[/color] 3:
[color=#2b91af]PortAccess[/color].Output(address, 12);
[color=#0000ff]break[/color];
[color=#0000ff]case[/color] 4:
[color=#2b91af]PortAccess[/color].Output(address, 4);
[color=#0000ff]break[/color];
[color=#0000ff]case[/color] 5:
[color=#2b91af]PortAccess[/color].Output(address, 6);
[color=#0000ff]break[/color];
[color=#0000ff]case[/color] 6:
[color=#2b91af]PortAccess[/color].Output(address, 2);
[color=#0000ff]break[/color];
[color=#0000ff]case[/color] 7:
[color=#2b91af]PortAccess[/color].Output(address, 3);
[color=#0000ff]break[/color];
}
}
halfstep += 1;
[color=#0000ff]if[/color] (halfstep == 8)
{
halfstep = 0;
}
}
}

try to only look at the values going out from the PortAccess command. Address is 0x378(parallel port).
I am outputting so that a 0 on a bit would give power to that phase
bit0=phase1
bit1=phase2
bit3=phase3
bit4=phase4
any help for this would be appreciated as technical support cannot solve the problem, and I am thinking the issue might be hardware, and not software(which is why i provided the code i used).
thanks

Eric Therriault
Computer Engineering Technology Student