Glitch Filter; Position Counter - NXP Semiconductors freescale KV4 Series Reference Manual

Table of Contents

Introduction

41.2.4 Glitch Filter

Because the logic of the quadrature decoder must sense transitions, the inputs are first run

through a glitch filter. This filter has a digital delay line sampling multiple time points on

the signal and verifying a stable new state before outputting this new state to the internal

logic. The sample rate of this delay line is programmable to adapt to a variety of signal

41.2.5 Edge Detect State Machine

The edge detect state machine looks for changes in the four possible states of the filtered

PHASEA and PHASEB inputs, calculating the direction of motion. This information is

formatted as Count_Up and Count_Down signals. These signals are routed into up to

three up/down counters:

2. Revolution counter

3. Position difference counter

41.2.6 Position Counter

The 32-bit position counter calculates up or down on every count pulse, generated by the

difference of PHASEA and PHASEB. This counter acts as an integrator, whose count

value is proportional to position. The direction of the count is determined by the count up

and count down signals. Position counters may be initialized to a predetermined value by

one of three different methods:

1. Software-triggered event

2. INDEX signal transition

3. HOME signal transition

The INDEX and HOME signals can be programmed to interrupt the processor. Whenever

the position counter is read, either UPOS or LPOS, a snapshot of the position counter, the

position difference counter, and the revolution counters are each placed into their

respective hold registers. The direction of the count is determined by Count_Up and

Count_Down signals.

KV4x Reference Manual, Rev. 2, 02/2015

Freescale Semiconductor, Inc.