MC9S08RC8 Datasheet, PDF (141/234 Pages) Freescale Semiconductor, Inc – Microcontrollers

Timer/PWM (TPM)
When background mode is active, the timer counter and the coherency mechanism are frozen such that the
buffer latches remain in the state they were in when the background mode became active even if one or
both bytes of the counter are read while background mode is active.
10.7.3 Timer Counter Modulo Registers (TPM1MODH:TPM1MODL)
The read/write TPM modulo registers contain the modulo value for the TPM counter. After the TPM
counter reaches the modulo value, the TPM counter resumes counting from $0000 at the next clock
(CPWMS = 0) or starts counting down (CPWMS = 1), and the overflow flag (TOF) becomes set. Writing
to TPM1MODH or TPM1MODL inhibits the TOF bit and overflow interrupts until the other byte is
written. Reset sets the TPM counter modulo registers to $0000, which results in a free-running timer
counter (modulo disabled).
7
6
5
4
3
2
R
Bit 15
14
13
12
11
10
W
1
0
9
Bit 8
Reset
0
0
0
0
0
0
0
0
Figure 10-8. Timer Counter Modulo Register High (TPM1MODH)
7
6
5
4
3
2
1
0
R
Bit 7
6
5
4
3
2
1
Bit 0
W
Reset
0
0
0
0
0
0
0
0
Figure 10-9. Timer Counter Modulo Register Low (TPM1MODL)
It is good practice to wait for an overflow interrupt so both bytes of the modulo register can be written well
before a new overflow. An alternative approach is to reset the TPM counter before writing to the TPM
modulo registers to avoid confusion about when the first counter overflow will occur.
MC9S08RC/RD/RE/RG Data Sheet, Rev. 1.11
Freescale Semiconductor
141