
Chapter 11 Timer/Pulse-Width Modulator (S08TPMV2)
MC9S08LC60 Series Data Sheet: Technical Data, Rev. 4
Freescale Semiconductor
203
11.3.2
Timer x Counter Registers (TPMxCNTH:TPMxCNTL)
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 byte is read. This allows coherent 16-bit reads in either order. The
coherency mechanism is automatically restarted by an MCU reset, a write of any value to TPMxCNTH or
TPMxCNTL, or any write to the timer status/control register (TPMxSC).
Reset clears the TPM counter registers.
Table 11-2. TPM Clock Source Selection
CLKSB:CLKSA
TPM Clock Source to Prescaler Input
0:0
No clock selected (TPMx disabled)
0:1
Bus rate clock (BUSCLK)
1:0
Fixed system clock (XCLK)
1:1
External source (TPMxCLK)1,2
1 The maximum frequency that is allowed as an external clock is one-fourth of the bus
frequency.
2 If the external clock input is shared with channel n and is selected as the TPM clock source,
the corresponding ELSnB:ELSnA control bits should be set to 0:0 so channel n does not try
to use the same pin for a conicting function.
Table 11-3. Prescale Divisor Selection
PS2:PS1:PS0
TPM Clock Source Divided-By
0:0:0
1
0:0:1
2
0:1:0
4
0:1:1
8
1:0:0
16
1:0:1
32
1:1:0
64
1:1:1
128
76543210
R
Bit 15
14
13
12
11
10
9
Bit 8
W
Any write to TPMxCNTH clears the 16-bit counter.
Reset
00000000
Figure 11-4. Timer x Counter Register High (TPMxCNTH)