MC908QB8CDWE Freescale Semiconductor, MC908QB8CDWE Datasheet - Page 179

• Manufacturer Part Number: MC908QB8CDWE
• Description: IC MCU 8BIT 8K FLASH 16-SOIC
• Manufacturer: Freescale Semiconductor
• Series: HC08r

Specifications of MC908QB8CDWE

• Core Processor: HC08
• Core Size: 8-Bit
• Speed: 8MHz
• Connectivity: SCI, SPI
• Peripherals: LVD, POR, PWM
• Number Of I /o: 13
• Program Memory Size: 8KB (8K x 8)
• Program Memory Type: FLASH
• Ram Size: 256 x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 10x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 16-SOIC (0.300", 7.5mm Width)
• Processor Series: HC08QB
• Core: HC08
• Data Bus Width: 8 bit
• Data Ram Size: 256 B
• Interface Type: SCI, SPI
• Maximum Clock Frequency: 8 MHz
• Number Of Programmable I/os: 14
• Number Of Timers: 4
• Operating Supply Voltage: 3 V to 5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Development Tools By Supplier: FSICEBASE, M68CBL05AE, DEMO908QB8, DEMO908QC16
• Minimum Operating Temperature: - 40 C
• On-chip Adc: 10 bit
• For Use With: DEMO908QB8 - BOARD DEMO FOR MC68HC908QB8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Eeprom Size: -
• Lead Free Status / Rohs Status: Details

16.3.4 Pulse Width Modulation (PWM)
By using the toggle-on-overflow feature with an output compare channel, the TIM can generate a PWM
signal. The value in the TIM counter modulo registers determines the period of the PWM signal. The
channel pin toggles when the counter reaches the value in the TIM counter modulo registers. The time
between overflows is the period of the PWM signal.
As
of the PWM signal. The time between overflow and output compare is the pulse width. Program the TIM
to clear the channel pin on output compare if the polarity of the PWM pulse is 1 (ELSxA = 0). Program the
TIM to set the pin if the polarity of the PWM pulse is 0 (ELSxA = 1).
The value in the TIM counter modulo registers and the selected prescaler output determines the
frequency of the PWM output The frequency of an 8-bit PWM signal is variable in 256 increments. Writing
$00FF (255) to the TIM counter modulo registers produces a PWM period of 256 times the internal bus
clock period if the prescaler select value is 000. See
The value in the TIM channel registers determines the pulse width of the PWM output. The pulse width of
an 8-bit PWM signal is variable in 256 increments. Writing $0080 (128) to the TIM channel registers
produces a duty cycle of 128/256 or 50%.
16.3.4.1 Unbuffered PWM Signal Generation
Any output compare channel can generate unbuffered PWM pulses as described in
Modulation
pulse width value over the old value currently in the TIM channel registers.
An unsynchronized write to the TIM channel registers to change a pulse width value could cause incorrect
operation for up to two PWM periods. For example, writing a new value before the counter reaches the
old value but after the counter reaches the new value prevents any compare during that PWM period.
Also, using a TIM overflow interrupt routine to write a new, smaller pulse width value may cause the
compare to be missed. The TIM may pass the new value before it is written to the timer channel
(TCHxH:TCHxL).
Freescale Semiconductor
Figure 16-3
(PWM). The pulses are unbuffered because changing the pulse width requires writing the new
POLARITY = 1
POLARITY = 0
(ELSxA = 0)
(ELSxA = 1)
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 output compares.
shows, the output compare value in the TIM channel registers determines the pulse width
TCHx
TCHx
OVERFLOW
Figure 16-3. PWM Period and Pulse Width
PULSE
WIDTH
MC68HC908QB8 Data Sheet, Rev. 3
PERIOD
COMPARE
OUTPUT
OVERFLOW
16.8.1 TIM Status and Control
COMPARE
OUTPUT
OVERFLOW
Functional Description
Register.
16.3.4 Pulse Width
COMPARE
OUTPUT
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