Datasheet

Appendix B Timer Pulse-Width Modulator (TPMV2)
MC9S08DN60 Series Data Sheet, Rev 3
Freescale Semiconductor 335
B.2.2 Timer 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 B-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 conflicting function.
Table B-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 B-3. Timer Counter Register High (TPMxCNTH)