diff --git a/docs/StepperModes.md b/docs/StepperModes.md
index 3c966a9..bbdea00 100644
--- a/docs/StepperModes.md
+++ b/docs/StepperModes.md
@@ -1,5 +1,7 @@
 # Stepper Motor Modes
 
+A typical 4-wire stepper motors has 2 independent sets of coils, *A* and *B*.  A driver chip, which usually contains two full-bridge circuits, controls the amount and direction of current flowing through each coil.  When one or both coils are energized, a magnetic field is created with a repeating pattern of peaks and valleys
+
 ![fullStep2](images/fullStepTwoPhase.png)
 
 ![fullStep1](images/fullStepOnePhase.png)