Microchip Technology dsPIC30F - Quadrature Decoder

dsPIC30F Family Reference Manual
DS70063C-page 16-10 © 2004 Microchip Technology Inc.
16.4 Quadrature Decoder
Position measurement modes are selected when QEIM2 = 1 (QEICON<10>).
When QEIM1 = 1 (QEICON<9>), the ‘x4’ measurement mode is selected and the QEI logic
clocks the position counter on both edges of the Phase A and Phase B input signals.
The ‘x4’ measurement mode provides for finer resolution data (more position counts) to
determine the encoder position.
Figure 16-6: Quadrature Decoder Signals in 4X Mode
When QEIM1 = 0, the ‘x2’ measurement mode is selected and the QEI logic only looks at the
rising and falling edge of the Phase A input for the position counter increment rate. Every rising
and falling edge of the Phase A signal causes the position counter to increment or decrement.
The Phase B signal is still utilized for the determination of the counter direction, exactly like the
x4 measurement mode.
Figure 16-7: Quadrature Decoder Signals in 2X Mode
+1 +1 +1 +1 +1 +1 +1 +1 +1 +1 -1 -1 -1 -1 -1 -1 -1 -1
QEA
QEB
count_clock
POSCNT
UPDN
-1
+1 +1 +1 +1 -1 -1 -1+1
QEA
QEB
count_clock
POSCNT
UPDN
-1