diff --git a/ledmatrix.py b/ledmatrix.py
index 889f6c4..26fa538 100755
--- a/ledmatrix.py
+++ b/ledmatrix.py
@@ -77,7 +77,7 @@ class LedMatrix:
 		# one step to the east, and then south to north, before the cycle
 		# starts over.
 		stride = self.stride
-		phys_addr =  ((x-1)%self.panelcolumn) + ((y-1)*self.panelcolumn) + (round_down((x-1)/self.panelcolumn) * self.panelcolumn * self.panelcolumn)
+		phys_addr =  ((x-1)%self.panelcolumn) + ((y-1)*self.panelcolumn) + (self.round_down((x-1)/self.panelcolumn) * self.panelcolumn * self.panelcolumn)
 					#MOD(x-1;panelCol) + ((y-1)*panelCol) + (FLOOR.MATH((x-1)/panelCol;1)*panelCol*panelRow)
 		# if x & 1:
 		# 	phys_addr += stride - 1 - y