SAM3X8E Atmel Corporation, SAM3X8E Datasheet - Page 888

• Manufacturer Part Number: SAM3X8E
• Manufacturer: Atmel Corporation

Figure 36-19. Quadrature Error Detection
36.6.14.4
888
888
MCK
Abnormally formatted optical disk strips (theoretical view)
PHA
PHB
PHA
PHB
resulting PHA, PHB electrical waveforms
PHA
PHB
QERR
SAM3X/A
SAM3X/A
Even with an abnorrmaly formatted disk, there is no occurence of PHA, PHB switching at the same time.
Position and Rotation Measurement
A quadrature error is also reported by the quadrature decoder logic. Rather than reporting an
error only when 2 edges occur at the same time on PHA and PHB, which is unlikely to occur in
real life, there is a report if the time difference between 2 edges on PHA, PHB is lower than a
predefined value. This predefined value is configurable and corresponds to (MAXFILT+1) *
tMCK ns. After being filtered there is no reason to have 2 edges closer than (MAXFILT+1) *
tMCK ns under normal mode of operation. In the instance an anomaly occurs, a quadrature error
is reported on QERR flag on TC_QISR register.
MAXFILT must be tuned according to several factors such as the system clock frequency
(MCK), type of rotary sensor and rotation speed to be achieved.
When POSEN is set in TC_BMR register, position is processed on channel 0 (by means of the
PHA,PHB edge detections) and motor revolutions are accumulated in channel 1 timer/counter
and can be read through TC_CV0 and/or TC_CV1 register if the IDX signal is provided on
TIOA1 input.
Channel 0 and 1 must be configured in capture mode (WAVE = 0 in TC_CMR0).
strip edge inaccurary due to disk etching/printing process
duration < MAXFILT
MAXFILT = 2
11057A–ATARM–17-Feb-12
11057A–ATARM–17-Feb-12