(00)
(10)
(11)
(01)
(A,B)=
QEPA
QEPB
eQEP signals
10
01
00
11
Increment
counter
Decrement
counter
Decrement
counter
Increment
counter
Decrement
counter
Decrement
counter
Increment
counter
Increment
counter
Quadrature Decoder Unit (QDU)
827
SPRUH22I – April 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
C28 Enhanced QEP (eQEP) Module
9.3.1.1
Quadrature Count Mode
The quadrature decoder generates the direction and clock to the position counter in quadrature count
mode.
Direction Decoding—
The direction decoding logic of the eQEP circuit determines which one of the
sequences (QEPA, QEPB) is the leading sequence and accordingly updates the direction
information in QEPSTS[QDF] bit.
and
show the direction decoding logic in
truth table and state machine form. Both edges of the QEPA and QEPB signals are sensed to
generate count pulses for the position counter. Therefore, the frequency of the clock generated by
the eQEP logic is four times that of each input sequence.
shows the direction decoding
and clock generation from the eQEP input signals.
Table 9-2. Quadrature Decoder Truth Table
.
Previous Edge
Present Edge
QDIR
QPOSCNT
QA
↑
QB
↑
UP
Increment
QB
↓
DOWN
Decrement
QA
↓
TOGGLE
Increment or Decrement
QA
↓
QB
↓
UP
Increment
QB
↑
DOWN
Decrement
QA
↑
TOGGLE
Increment or Decrement
QB
↑
QA
↑
DOWN
Increment
QA
↓
UP
Decrement
QB
↓
TOGGLE
Increment or Decrement
QB
↓
QA
↓
DOWN
Increment
QA
↑
UP
Decrement
QB
↑
TOGGLE
Increment or Decrement
Figure 9-6. Quadrature Decoder State Machine