Quadrature Decoder State Machine; Quadrature Decoder Truth Table - Texas Instruments Concerto F28M35 Series Technical Reference Manual

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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.
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.
and clock generation from the eQEP input signals.
.
Previous Edge
QA↑
QA↓
QB↑
QB↓
(00)
(A,B)=
(10)
QEPA
QEPB
eQEP signals
SPRUH22I – April 2012 – Revised November 2019
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Table 9-2
Table 9-2. Quadrature Decoder Truth Table
Present Edge
QB↑
QB↓
QA↓
QB↓
QB↑
QA↑
QA↑
QA↓
QB↓
QA↓
QA↑
QB↑
Figure 9-6. Quadrature Decoder State Machine
Increment
counter
(11)
(01)
Increment
counter
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and Figure 9-6 show the direction decoding logic in
Figure 9-7 shows the direction decoding
QDIR QPOSCNT
UP Increment
DOWN Decrement
TOGGLE Increment or Decrement
UP Increment
DOWN Decrement
TOGGLE Increment or Decrement
DOWN Increment
UP Decrement
TOGGLE Increment or Decrement
DOWN Increment
UP Decrement
TOGGLE Increment or Decrement
10
Decrement Decrement
counter counter
00
Decrement Decrement
counter counter
01
C28 Enhanced QEP (eQEP) Module
Quadrature Decoder Unit (QDU)
Increment
counter
11
Increment
counter
827