MC9S12HZ128VAL Datasheet, PDF (291/692 Pages) Freescale Semiconductor, Inc – MC9S12HZ256 Data Sheet, Rev. 2.05

Chapter 10
Stepper Stall Detector (SSDV1)
10.1 Introduction
The stepper stall detector (SSD) block provides a circuit to measure and integrate the induced voltage on
the non-driven coil of a stepper motor using full steps when the gauge pointer is returning to zero (RTZ).
During the RTZ event, the pointer is returned to zero using full steps in either clockwise or counter
clockwise direction, where only one coil is driven at any point in time. The back electromotive force
(EMF) signal present on the non-driven coil is integrated after a blanking time, and its results stored in a
16-bit accumulator. The 16-bit modulus down counter can be used to monitor the blanking time and the
integration time. The value in the accumulator represents the change in linked flux (magnetic flux times
the number of turns in the coil) and can be compared to a stored threshold. Values above the threshold
indicate a moving motor, in which case the pointer can be advanced another full step in the same direction
and integration be repeated. Values below the threshold indicate a stalled motor, thereby marking the
cessation of the RTZ event. The SSD is capable of multiplexing two stepper motors.
10.1.1 Modes of Operation
• Return to zero modes
— Blanking with no drive
— Blanking with drive
— Conversion
— Integration
• Low-power modes
10.1.2 Features
• Programmable full step state
• Programmable integration polarity
• Blanking (recirculation) state
• 16-bit integration accumulator register
• 16-bit modulus down counter with interrupt
• Multiplex two stepper motors
MC9S12HZ256 Data Sheet, Rev. 2.05
Freescale Semiconductor
291