MC908AZ32ACFU Freescale Semiconductor, MC908AZ32ACFU Datasheet - Page 193

• Manufacturer Part Number: MC908AZ32ACFU
• Description: IC MCU 32K FLASH 8.4MHZ 64-QFP
• Manufacturer: Freescale Semiconductor
• Series: HC08r

Specifications of MC908AZ32ACFU

• Core Processor: HC08
• Core Size: 8-Bit
• Speed: 8MHz
• Connectivity: CAN, SCI, SPI
• Peripherals: LVD, POR, PWM
• Number Of I /o: 40
• Program Memory Size: 32KB (32K x 8)
• Program Memory Type: FLASH
• Eeprom Size: 512 x 8
• Ram Size: 1K x 8
• Voltage - Supply (vcc/vdd): 4.5 V ~ 5.5 V
• Data Converters: A/D 15x8b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 64-QFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

An unsynchronized write to the TIMA 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 TIMA overflow interrupt routine to write a new, smaller pulse width value may cause
the compare to be missed. The TIMA may pass the new value before it is written to the TIMA channel
registers.
Use the following methods to synchronize unbuffered changes in the PWM pulse width on channel x:
18.3.4.2 Buffered PWM Signal Generation
Channels 0 and 1 can be linked to form a buffered PWM channel whose output appears on the
PTE2/TCH0 pin. The TIMA channel registers of the linked pair alternately control the pulse width of the
output.
Setting the MS0B bit in TIMA channel 0 status and control register (TASC0) links channel 0 and
channel 1. The TIMA channel 0 registers initially control the pulse width on the PTE2/TCH0 pin. Writing
to the TIMA channel 1 registers enables the TIMA channel 1 registers to synchronously control the pulse
width at the beginning of the next PWM period. At each subsequent overflow, the TIMA channel registers
(0 or 1) that control the pulse width are the ones written to last. TASC0 controls and monitors the buffered
PWM function and TIMA channel 1 status and control register (TASC1) is unused. While the MS0B bit is
set, the channel 1 pin, PTE3/TCH1, is available as a general-purpose I/O pin.
Channels 2 and 3 can be linked to form a buffered PWM channel whose output appears on the
PTF0/TCH2 pin. The TIMA channel registers of the linked pair alternately control the pulse width of the
output.
Setting the MS2B bit in TIMA channel 2 status and control register (TASC2) links channel 2 and
channel 3. The TIMA channel 2 registers initially control the pulse width on the PTF0/TCH2 pin. Writing
to the TIMA channel 3 registers enables the TIMA channel 3 registers to synchronously control the pulse
width at the beginning of the next PWM period. At each subsequent overflow, the TIMA channel registers
(2 or 3) that control the pulse width are the ones written to last. TASC2 controls and monitors the buffered
PWM function and TIMA channel 3 status and control register (TASC3) is unused. While the MS2B bit is
set, the channel 3 pin, PTF1/TCH3, is available as a general-purpose I/O pin.
Freescale Semiconductor
•
•
When changing to a shorter pulse width, enable channel x output compare interrupts and write the
new value in the output compare interrupt routine. The output compare interrupt occurs at the end
of the current pulse. The interrupt routine has until the end of the PWM period to write the new
value.
When changing to a longer pulse width, enable TIMA overflow interrupts and write the new value
in the TIMA overflow interrupt routine. The TIMA overflow interrupt occurs at the end of the current
PWM period. Writing a larger value in an output compare interrupt routine (at the end of the current
pulse) could cause two output compares to occur in the same PWM period.
In PWM signal generation, do not program the PWM channel to toggle on
output compare. Toggling on output compare prevents reliable 0% duty
cycle generation and removes the ability of the channel to self-correct in the
event of software error or noise. Toggling on output compare also can
cause incorrect PWM signal generation when changing the PWM pulse
width to a new, much larger value.
MC68HC908AZ32A Data Sheet, Rev. 2
NOTE
Functional Description
193