Timer Interface Module (TIM2)
Functional Description
MC68HC908GR60A MC68HC908GR48A MC68HC908GR32A
Data Sheet
MOTOROLA
Timer Interface Module (TIM2)
281
Channels 2 and 3 can be linked to form a buffered PWM channel whose output
appears on the T2CH2 pin. The TIM2 channel registers of the linked pair
alternately control the pulse width of the output.
Setting the MS2B bit in TIM2 channel 2 status and control register (T2SC2) links
channel 2 and channel 3. The TIM2 channel 2 registers initially control the pulse
width on the T2CH2 pin. Writing to the TIM2 channel 3 registers enables the TIM2
channel 3 registers to synchronously control the pulse width at the beginning of the
next PWM period. At each subsequent overflow, the TIM2 channel registers
(2 or 3) that control the pulse width are the ones written to last. T2SC2 controls and
monitors the buffered PWM function, and TIM2 channel 3 status and control
register (T2SC3) is unused. While the MS2B bit is set, the channel 3 pin, T2CH3,
is available as a general-purpose I/O pin.
Channels 4 and 5 can be linked to form a buffered PWM channel whose output
appears on the T2CH4 pin. The TIM2 channel registers of the linked pair
alternately control the pulse width of the output.
Setting the MS4B bit in TIM2 channel 4 status and control register (T2SC4) links
channel 4 and channel 5. The TIM2 channel 4 registers initially control the pulse
width on the T2CH4 pin. Writing to the TIM2 channel 5 registers enables the TIM2
channel 5 registers to synchronously control the pulse width at the beginning of the
next PWM period. At each subsequent overflow, the TIM2 channel registers
(4 or 5) that control the pulse width are the ones written to last. T2SC4 controls and
monitors the buffered PWM function, and TIM2 channel 5 status and control
register (T2SC5) is unused. While the MS4B bit is set, the channel 5 pin, T2CH5,
is available as a general-purpose I/O pin.
NOTE:
In buffered PWM signal generation, do not write pulse width values to the currently
active channel registers. User software should track the currently active channel to
prevent writing a new value to the active channel. Writing to the active channel
registers is the same as generating unbuffered PWM signals.
18.3.4.3 PWM Initialization
To ensure correct operation when generating unbuffered or buffered PWM signals,
use the following initialization procedure:
1.
In the TIM2 status and control register (T2SC):
a.
Stop the TIM2 counter by setting the TIM2 stop bit, TSTOP.
b.
Reset the TIM2 counter and prescaler by setting the TIM2 reset bit,
TRST.
2.
In the TIM2 counter modulo registers (T2MODH:T2MODL), write the value
for the required PWM period.
3.
In the TIM2 channel x registers (T2CHxH:T2CHxL), write the value for the
required pulse width.