NXP Semiconductors freescale KV4 Series, Reference Manual

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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 39-169. Example of FTM up and signed counting
Table 39-243. 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.
Functional description
KV4x Reference Manual, Rev. 2, 02/2015
950
Preliminary
Freescale Semiconductor, Inc.