mcf51ac256a Freescale Semiconductor, Inc, mcf51ac256a Datasheet - Page 210

• Manufacturer Part Number: mcf51ac256a
• Description: Mcf51ac Flexis
• Manufacturer: Freescale Semiconductor, Inc

FlexTimer Module (FTMV1)
11.3.4
The two read-only FTM counter registers contain the high and low bytes of the value in the FTM counter.
Reading either byte (FTMxCNTH or FTMxCNTL) latches the contents of both bytes into a buffer where
they remain latched until the other half is read. This allows coherent 16-bit reads in either big-endian or
little-endian order which makes this more friendly to various compiler implementations. The coherency
mechanism is automatically restarted by an MCU reset or any write to the FTM status and control register
(FTMxSC).
Reset clears the FTM counter registers. Writing any value to FTMxCNTH or FTMxCNTL updates the
FTM counter (FTMxCNTH:FTMxCNTL) with its initial value (FTMxCNTINH:FTMxCNTINL)and
resets the read coherency mechanism, regardless of the data involved in the write.
11-10
Reset
W
R
Bit 15
FTM Counter Registers (FTMxCNTH:FTMxCNTL)
0
7
Any write to FTMxCNTH updates the 16-bit counter with its initial value (FTMxCNTINH:FTMxCNTINL)
MCF51AC256 ColdFire Integrated Microcontroller Reference Manual, Rev. 5
14
0
6
CLKS
Figure 11-3. FTM Counter Register High (FTMxCNTH)
00
01
10
11
000
001
010
011
100
101
110
111
PS
Table 11-4. FTM Clock Source Selection
Table 11-5. Prescale Factor Selection
13
5
0
FTMEN
X
X
X
0
1
FTM Clock Source Divided-by
12
0
4
No clock selected (FTM counter disable)
FTM Clock Source to Prescaler Input
System clock divided by 2 (for TPM
Fixed system clock
128
16
32
64
External source
1
2
4
8
compatibility)
System clock
11
0
3
10
0
2
Freescale Semiconductor
1
9
0
Bit 8
0
0