diff --git a/adafruit_trellism4.py b/adafruit_trellism4.py
index 6394e6b..9a65899 100644
--- a/adafruit_trellism4.py
+++ b/adafruit_trellism4.py
@@ -68,6 +68,8 @@ def __init__(self, pin, *, width, height, rotation=0):
     def __setitem__(self, index, value):
         if not isinstance(index, tuple) or len(index) != 2:
             raise IndexError("Index must be tuple")
+        if index[0] >= self.width or index[1] >= self.height:
+            raise IndexError("Pixel assignment outside available coordinates.")
 
         if self._rotation == 0 or self._rotation == 180:
             offset = self.width * index[1] + index[0]
@@ -78,6 +80,9 @@ def __setitem__(self, index, value):
         elif self._rotation == 90:
             offset = self.height * (self.width - index[0] - 1) + index[1]
 
+        if offset < 0:
+            raise IndexError("Pixel assignment outside available coordinates.")
+
         self._neopixel[offset] = value
         self._neopixel.show()
 
@@ -267,9 +272,9 @@ def __init__(self, rotation=0):
             row = []
             for x in range(4):
                 if rotation == 0:
-                    coord = (x, y)
+                    coord = (y, x)
                 elif rotation == 180:
-                    coord = (3 - x, 7 - y)
+                    coord = (7 - y, 3 - x)
                 elif rotation == 90:
                     coord = (3 - x, y)
                 elif rotation == 270:
diff --git a/examples/neopixel_trellism4.simpletest.py b/examples/neopixel_trellism4.simpletest.py
index f9219e8..1381a47 100755
--- a/examples/neopixel_trellism4.simpletest.py
+++ b/examples/neopixel_trellism4.simpletest.py
@@ -30,7 +30,7 @@ def wheel(pos):
     for press in pressed - current_press:
         if press:
             print("Pressed:", press)
-            pixel = (press[0] * 8) + press[1]
+            pixel = (press[1] * 8) + press[0]
             pixel_index = (pixel * 256 // 32)
             trellis.pixels.fill(wheel(pixel_index & 255))
     for release in current_press - pressed: