+1 +1
+1
+1
+1
+1
+1
−1 −1
−1
−1
−1
−1
−1
−1
−1
−1
−1
+1
+1
+1
−1 −1 −1 −1 −1 −1
−1
+1 +1 +1 +1 +1 +1
+1
+1
+1
+1
+1
−1
−1
−1
QA
QB
QCLK
QDIR
QPOSCNT
QA
QB
QCLK
QDIR
QPOSCNT
Figure 7-7. Quadrature-clock and Direction Decoding
Phase Error Flag
In normal operating conditions, quadrature inputs QEPA and QEPB will be 90 degrees
out of phase. The phase error flag (PHE) is set in the QFLG register and the QPOSCNT
value can be incorrect and offset by multiples of 1 or 3. That is, when edge transition is
detected simultaneously on the QEPA and QEPB signals to optionally generate interrupts.
State transitions marked by dashed lines in
are invalid transitions that generate a
phase error.
Count
Multiplication
The eQEP position counter provides 4x times the resolution of an input clock by generating
a quadrature-clock (QCLK) on the rising/falling edges of both eQEP input clocks (QEPA and
QEPB) as shown in
Reverse Count
In normal quadrature count operation, QEPA input is fed to the QA input of the quadrature
decoder and the QEPB input is fed to the QB input of the quadrature decoder. Reverse
counting is enabled by setting the SWAP bit in the QDECCTL register. This will swap the
input to the quadrature decoder, thereby reversing the counting direction.
7.4.1.2 Direction-Count Mode
Some position encoders provide direction and clock outputs, instead of quadrature outputs. In such cases,
direction-count mode can be used. QEPA input will provide the clock for the position counter and the QEPB input
will have the direction information. The position counter is incremented on every rising edge of a QEPA input
when the direction input is high, and decremented when the direction input is low.
Enhanced Quadrature Encoder Pulse (eQEP)
470
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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