Datasheet

SAM3X / SAM3A [DATASHEET]
Atmel-11057C-ATARM-SAM3X-SAM3A-Datasheet_23-Mar-15
876
configurable and corresponds to (MAXFILT + 1) × t
peripheral clock
ns. After being filtered there is no reason to have
two edges closer than (MAXFILT + 1) × t
peripheral clock
ns under normal mode of operation.
Figure 36-19. Quadrature Error Detection
MAXFILT must be tuned according to several factors such as the peripheral clock frequency, type of rotary sensor
and rotation speed to be achieved.
36.6.14.4 Position and Rotation Measurement
When the POSEN bit is set in the TC_BMR, the motor axis position is processed on channel 0 (by means of the
PHA, PHB edge detections) and the number of motor revolutions are recorded on channel 1 if the IDX signal is
provided on the TIOB1 input. The position measurement can be read in the TC_CV0 register and the rotation
measurement can be read in the TC_CV1 register.
Channel 0 and 1 must be configured in Capture mode (TC_CMR0.WAVE = 0). ‘Rising edge’ must be selected as
the External Trigger Edge (TC_CMR.ETRGEDG = 0x01) and ‘TIOA’ must be selected as the External Trigger
(TC_CMR.ABETRG = 0x1).
In parallel, the number of edges are accumulated on timer/counter channel 0 and can be read on the TC_CV0
register.
Therefore, the accurate position can be read on both TC_CV registers and concatenated to form a 32-bit word.
The timer/counter channel 0 is cleared for each increment of IDX count value.
Peripheral Clock
MAXFILT = 2
PHA
PHB
A
bnormally formatted optical disk strips (theoretical view)
PHA
PHB
strip edge inaccurary due to disk etching/printing process
resulting PHA, PHB electrical waveforms
PHA
PHB
Even with an abnorrmaly formatted disk, there is no occurence of PHA, PHB switching at the same time.
QERR
duration < MAXFILT