mcf51ac256a Freescale Semiconductor, Inc, mcf51ac256a Datasheet - Page 481

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

21.3.2
The two read-only TPM counter registers contain the high and low bytes of the value in the TPM counter.
Reading either byte (TPMxCNTH or TPMxCNTL) 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 big-endian or
little-endian order that makes this more friendly to various compiler implementations. The coherency
mechanism is automatically restarted by an MCU reset or any write to the timer status/control register
(TPMxSC).
Reset clears the TPM counter registers. Writing any value to TPMxCNTH or TPMxCNTL also clears the
TPM counter (TPMxCNTH:TPMxCNTL) and resets the coherency mechanism, regardless of the data
involved in the write.
Freescale Semiconductor
Reset
W
R
TPM-Counter Registers (TPMxCNTH:TPMxCNTL)
0
7
MCF51AC256 ColdFire Integrated Microcontroller Reference Manual, Rev. 5
0
6
Figure 21-7. TPM Counter Register High (TPMxCNTH)
CLKSB:CLKSA
PS[2:0]
000
001
010
011
100
101
110
111
01
10
11
Table 21-4. Prescale Factor Selection
Any write to TPMxCNTH clears the 16-bit counter
Table 21-3. TPM Clock Selection
0
5
TPM Clock to Prescaler Input
TPMxCNT[15:8]
0
4
TPM Clock Divided-by
Fixed frequency clock
External clock
Bus clock
128
16
32
64
1
2
4
8
0
3
0
2
Timer/PWM Module (TPMV3)
1
0
0
0
21-9