MC9S08GB60 Datasheet, PDF (161/290 Pages) Motorola, Inc – Microcontrollers

TPM Registers and Control Bits
TOF — Timer Overflow Flag
This flag is set when the TPM counter changes to $0000 after reaching the modulo value programmed
in the TPM counter modulo registers. When the TPM is configured for CPWM, TOF is set after the
counter has reached the value in the modulo register, at the transition to the next lower count value.
Clear TOF by reading the TPM status and control register when TOF is set and then writing a 0 to TOF.
If another TPM overflow occurs before the clearing sequence is complete, the sequence is reset so TOF
would remain set after the clear sequence was completed for the earlier TOF. Reset clears the TOF bit.
Writing a 1 to TOF has no effect.
1 = TPM counter has overflowed.
0 = TPM counter has not reached modulo value or overflow.
TOIE — Timer Overflow Interrupt Enable
This read/write bit enables TPM overflow interrupts. If TOIE is set, an interrupt is generated when
TOF equals 1. Reset clears TOIE.
1 = TOF interrupts enabled.
0 = TOF interrupts inhibited (use software polling).
CPWMS — Center-Aligned PWM Select
This read/write bit selects CPWM operating mode. Reset clears this bit so the TPM operates in
up-counting mode for input capture, output compare, and edge-aligned PWM functions. Setting
CPWMS reconfigures the TPM to operate in up-/down-counting mode for CPWM functions. Reset
clears the CPWMS bit.
1 = All TPMx channels operate in center-aligned PWM mode.
0 = All TPMx channels operate as input capture, output compare, or edge-aligned PWM mode as
selected by the MSnB:MSnA control bits in each channel’s status and control register.
CLKSB:CLKSA — Clock Source Select
As shown in Table 10-1, this 2-bit field is used to disable the TPM system or select one of three clock
sources to drive the counter prescaler. The external source and the XCLK are synchronized to the bus
clock by an on-chip synchronization circuit.
Table 10-1. TPM Clock Source Selection
CLKSB:CLKSA
TPM Clock Source to Prescaler Input
0:0
No clock selected (TPM disabled)
0:1
Bus rate clock (BUSCLK)
1:0
Fixed system clock (XCLK)
1:1
External source (TPMx Ext Clk)¹,²
1. The maximum frequency that is allowed as an external clock is one-fourth of the bus
frequency.
2. When the TPMxCH0 pin is selected as the TPM clock source, the corresponding
ELS0B:ELS0A control bits should be set to 0:0 so channel 0 does not try to use the same pin
for a conflicting function.
MC9S08GB/GT Data Sheet, Rev. 2.3
Freescale Semiconductor
161