Limiting KeyDown

I use the KeyDown function to move a character across the screen. But when you press two keys at the same time eg. up and right, the character will move diagonally. How do you limit the character to moving along one axis at a time?

I think like this:

rx = keydown(205) - keydown(203)
if rx <> 0 then
   x = x + rx
else
   y = y + keydown(200) - keydown(208)
end if

(edit:) wait, this one is better:

Graphics 800, 600, 0, 2
SetBuffer BackBuffer()

x = 400
y = 300


Repeat

	;white
	Color 255,255,255
	Oval x - 5, y - 5, 11, 11

	;find out if a key is pressed for the first time	
	If Not(down1 Or down2) Then 
		down1 = KeyHit(203) Or KeyHit(205)
		down2 = KeyHit(200) Or KeyHit(208)
	End If

	;read directions	
	rx = KeyDown(205) - KeyDown(203)
	ry = KeyDown(200) - KeyDown(208)

	;if movement stops, reset flags
	If rx = 0 Then down1 = 0
	If ry = 0 Then down2 = 0

	;limit to one direction	
	If down1 Then ry = 0
	If down2 Then rx = 0
	
	;apply direction
	x = x + rx
	y = y + ry

	;red	
	Color 255,0,0
	Oval x - 5, y - 5, 11, 11
	
	Flip
	
Until KeyHit(1)

End

The below code limits movement to a single axis giving preference to the y axis. Arrange it with left and right first and you will give preference to the x axis.

; I make UP, DOWN, LEFT, RIGHT global variables that can be defined as any key. 
;This is great as it allows for user defined keyboard set ups.

If keydown(UP) Then
 ; add code here to move object accordingly
ElseIf keydown(DOWN) Then
 ; add code here to move object accordingly
ElseIf keydown(LEFT) Then
 ; add code here to move object accordingly
ElseIf keydown(RIGHT) Then
 ; add code here to move object accordingly
EndIf

Thanks for the help. It now works.