MC9S08GB60A Datasheet, PDF (158/302 Pages) Freescale Semiconductor, Inc – HCS08 Microcontrollers

Timer/PWM (TPM)
counter (when operating in normal up-counting mode) provides the timing reference for the input capture,
output compare, and edge-aligned PWM functions. The timer counter modulo registers,
TPMxMODH:TPMxMODL, control the modulo value of the counter. (The values $0000 or $FFFF
effectively make the counter free running.) Software can read the counter value at any time without
affecting the counting sequence. Any write to either byte of the TPMxCNT counter resets the counter
regardless of the data value written.
All TPM channels are programmable independently as input capture, output compare, or buffered
edge-aligned PWM channels.
10.4 Pin Descriptions
Table 10-2 shows the MCU pins related to the TPM modules. When TPMxCH0 is used as an external
clock input, the associated TPM channel 0 can not use the pin. (Channel 0 can still be used in output
compare mode as a software timer.) When any of the pins associated with the timer is configured as a timer
input, a passive pullup can be enabled. After reset, the TPM modules are disabled and all pins default to
general-purpose inputs with the passive pullups disabled.
10.4.1 External TPM Clock Sources
When control bits CLKSB:CLKSA in the timer status and control register are set to 1:1, the prescaler and
consequently the 16-bit counter for TPMx are driven by an external clock source connected to the
TPMxCH0 pin. A synchronizer is needed between the external clock and the rest of the TPM. This
synchronizer is clocked by the bus clock so the frequency of the external source must be less than one-half
the frequency of the bus rate clock. The upper frequency limit for this external clock source is specified to
be one-fourth the bus frequency to conservatively accommodate duty cycle and phase-locked loop (PLL)
or frequency-locked loop (FLL) frequency jitter effects.
When the TPM is using the channel 0 pin for an external clock, the corresponding ELS0B:ELS0A control
bits should be set to 0:0 so channel 0 is not trying to use the same pin.
10.4.2 TPMxCHn — TPMx Channel n I/O Pins
Each TPM channel is associated with an I/O pin on the MCU. The function of this pin depends on the
configuration of the channel. In some cases, no pin function is needed so the pin reverts to being controlled
by general-purpose I/O controls. When a timer has control of a port pin, the port data and data direction
registers do not affect the related pin(s). See the Pins and Connections chapter for additional information
about shared pin functions.
10.5 Functional Description
All TPM functions are associated with a main 16-bit counter that allows flexible selection of the clock
source and prescale divisor. A 16-bit modulo register also is associated with the main 16-bit counter in the
TPM. Each TPM channel is optionally associated with an MCU pin and a maskable interrupt function.
The TPM has center-aligned PWM capabilities controlled by the CPWMS control bit in TPMxSC. When
CPWMS is set to 1, timer counter TPMxCNT changes to an up-/down-counter and all channels in the
MC9S08GB60A Data Sheet, Rev. 2
158
Freescale Semiconductor