Information

phase B (counting direction)
phase A (counting rate)
FTM counter
increment/decrement
FTM counter
MOD
CNTIN
0x0000
Time
+1
+1
+1
+1
+1
+1
+1
+1
-1
-1
-1
-1
-1
Figure 35-210. Quadrature Decoder – Count and Direction Encoding mode
If QUADMODE = 0, then the Phase A and Phase B Encoding mode is enabled; see the
following figure. In this mode, the relationship between phase A and B signals indicates
the counting direction, and phase A and B signals define the counting rate. The FTM
counter is updated when there is an edge either at the phase A or phase B signals.
If PHAPOL = 0 and PHBPOL = 0, then the FTM counter increment happens when:
• there is a rising edge at phase A signal and phase B signal is at logic zero;
• there is a rising edge at phase B signal and phase A signal is at logic one;
• there is a falling edge at phase B signal and phase A signal is at logic zero;
• there is a falling edge at phase A signal and phase B signal is at logic one;
and the FTM counter decrement happens when:
• there is a falling edge at phase A signal and phase B signal is at logic zero;
• there is a falling edge at phase B signal and phase A signal is at logic one;
• there is a rising edge at phase B signal and phase A signal is at logic zero;
• there is a rising edge at phase A signal and phase B signal is at logic one.
Chapter 35 FlexTimer Module (FTM)
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
Freescale Semiconductor, Inc. 809