Freescale Semiconductor MCF51QE128RM Reset Overview, General, Description of Reset Operation

Timer/PWM Module (S08TPMV3)

Input capture, output compare, and edge-aligned PWM functions do not make sense when the counter is operating in up/down counting mode so this implies that all active channels within a TPM must be used in CPWM mode when CPWMS is set.

Because the TPM is connected to an 8-bit peripheral bus, the settings in the timer channel registers are buffered to ensure coherent 16-bit updates and to avoid unexpected PWM pulse widths. Writes to TPMxMODH, TPMxMODL, TPMxCnVH, and TPMxCnVL, actually write to buffer registers.

In center-aligned PWM mode, the TPMxCnVH:L registers are updated with the value of their write buffer according to the value of CLKSB:CLKSA bits:

•If CLKSB and CLKSA are cleared, the registers are updated when the second byte is written

•If CLKSB and CLKSA are not cleared, the registers are updated after both bytes are written, and the TPM counter changes from TPMxMODH:TPMxMODL − 1 to TPMxMODH:TPMxMODL. If the TPM counter is a free-running counter, the update is made when the TPM counter changes from 0xFFFE to 0xFFFF.

When TPMxCNTH:TPMxCNTL equals TPMxMODH:TPMxMODL, the TPM optionally generates a TOF interrupt at the end of this count.

Writing to TPMxSC cancels any values written to TPMxMODH and/or TPMxMODL and resets the coherency mechanism for the modulo registers. Writing to TPMxCnSC cancels any values written to the channel value registers and resets the coherency mechanism for TPMxCnVH:TPMxCnVL.

17.5Reset Overview

17.5.1General

The TPM is reset whenever any MCU reset occurs.

17.5.2Description of Reset Operation

Reset clears TPMxSC, which disables clocks to the TPM and disables timer overflow interrupts (TOIE = 0). CPWMS, MSnB, MSnA, ELSnB, and ELSnA are all cleared. This configures all TPM channels for input-capture operation with the associated pins disconnected from I/O pin logic (all MCU pins related to the TPM revert to general purpose I/O pins).

17.6Interrupts

17.6.1General

The TPM generates an optional interrupt for the main counter overflow and an interrupt for each channel. The meaning of channel interrupts depends on each channel’s mode of operation. If the channel is configured for input capture, the interrupt flag is set each time the selected input capture edge is recognized. If the channel is configured for output compare or PWM modes, the interrupt flag is set each time the main timer counter matches the value in the 16-bit channel value register.

MCF51QE128 MCU Series Reference Manual, Rev. 3

352 Freescale Semiconductor

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