NXP Semiconductors K22F series, Reference Manual, Page: 949 / 1407

CNTIN defines the starting value of the count and MOD defines the final value of the
count, see the following figure. The value of CNTIN is loaded into the FTM counter, and
the counter increments until the value of MOD is reached, at which point the counter is
reloaded with the value of CNTIN.
The FTM period when using up counting is (MOD – CNTIN + 0x0001) × period of the
FTM counter clock.
The TOF bit is set when the FTM counter changes from MOD to CNTIN.
FTM counting is up.
FTM counter (in decimal values)
period of FTM counter clock
MOD = 0x0004
TOF bit
set TOF bit
set TOF bit
set TOF bit
4 -4 -3 -2 -1 -4 -3 -2 -1
0 1 2 3 4 0 1 2 3 4 -4 -3
CNTIN = 0xFFFC (in two's complement is equal to -4)
period of counting = (MOD - CNTIN + 0x0001) x period of FTM counter clock
Figure 39-4. Example of FTM up and signed counting
Table 39-4. FTM counting based on CNTIN value
When Then
CNTIN = 0x0000 The FTM counting is equivalent to TPM up counting, that is,
up and unsigned counting. See the following figure.
CNTIN[15] = 1 The initial value of the FTM counter is a negative number in
two's complement, so the FTM counting is up and signed.
CNTIN[15] = 0 and CNTIN ≠ 0x0000 The initial value of the FTM counter is a positive number, so
the FTM counting is up and unsigned.
Chapter 39 FlexTimer Module (FTM)
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
NXP Semiconductors 949