(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
Basic Operation
1964
SPNU563A – March 2018
Copyright © 2018, Texas Instruments Incorporated
Enhanced Quadrature Encoder Pulse (eQEP) Module
34.2.2.2.1.1 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 34-2. 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 34-6. Quadrature Decoder State Machine