MC68331CEH25 Freescale Semiconductor, MC68331CEH25 Datasheet - Page 175

• Manufacturer Part Number: MC68331CEH25
• Description: IC MCU 32BIT 25MHZ 132-PQFP
• Manufacturer: Freescale Semiconductor
• Series: M683xxr

Specifications of MC68331CEH25

• Core Processor: CPU32
• Core Size: 32-Bit
• Speed: 25MHz
• Connectivity: EBI/EMI, SCI, SPI, UART/USART
• Peripherals: POR, PWM, WDT
• Number Of I /o: 18
• Program Memory Type: ROMless
• Voltage - Supply (vcc/vdd): 4.5 V ~ 5.5 V
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 132-QFP
• Controller Family/series: 68K
• No. Of I/o's: 18
• Cpu Speed: 25MHz
• No. Of Timers: 1
• Embedded Interface Type: QSPI, SCI, UART
• No. Of Pwm Channels: 2
• Digital Ic Case Style: PQFP
• Rohs Compliant: Yes
• Processor Series: M683xx
• Core: CPU32
• Data Bus Width: 32 bit
• Data Ram Size: 80 B
• Interface Type: QSPI, SCI, UART
• Maximum Clock Frequency: 25 MHz
• Number Of Programmable I/os: 18
• Number Of Timers: 1
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Eeprom Size: -
• Ram Size: -
• Program Memory Size: -
• Data Converters: -
• Lead Free Status / Rohs Status: Details

7.11.2 PWM Function
MC68331
USER’S MANUAL
The PWM count register (PWMCNT) can be read at any time without affecting its val-
ue. A read must be a word access to ensure coherence, but byte accesses can be
made if coherence is not needed. The counter is cleared to $0000 during reset and is
a read-only register except in freeze or test mode.
Fifteen of the sixteen counter bits are output to multiplexers A and B. The multiplexers
provide the fast and slow modes of the PWM unit. Mode for PWMA is selected by the
SFA bit in the PWM control register C (PWMC). Mode for PWMB is selected by the
SFB bit in the same register.
PWMA, PWMB, and PPR[2:0] bits in PWMC control PWM output frequency. In fast
mode, bits [7:0] of PWMCNT are used to clock the PWM logic; in slow mode, bits [14:7]
are used. The period of a PWM output in is 128 times longer than the fast mode period.
Table 7-3 shows a range of PWM output frequencies using a 16.78-MHz system clock
and 20.97-MHz system clock.
The pulse width values of the PWM outputs are determined by control registers PWMA
and PWMB. PWMA and PWMB are 8-bit registers implemented as two bytes of a 16-
bit register. PWMA and PWMB can be accessed as separate bytes or as one 16-bit
register. A value of $00 loaded into either register causes the corresponding output pin
to output a continuous logic level zero signal. A value of $80 causes the corresponding
output signal to have a 50% duty cycle, and so on, to the maximum value of $FF, which
corresponds to an output which is at logic level one for 255/256 of the cycle.
Setting the F1A (for PWMA) or F1B (for PWMB) bits in the register causes the corre-
sponding pin to output a continuous logic level one signal. The logic level of the asso-
ciated pin does not change until the end of the current cycle. F1A and F1B are the
lower two bits of CFORC, but can be accessed at the same word address as PWMC.
Data written to PWMA and PWMB is not used until the end of a complete cycle. This
prevents spurious short or long pulses when register values are changed. The current
duty cycle value is stored in the appropriate PWM buffer register (PWMBUFA or PW-
MBUFB). The new value is transferred from the PWM register to the buffer register at
the end of the current cycle.
PPR
[2:0]
000
001
010
011
100
101
110
111
Div 16 = 1.05 MHz Div 16 = 1.31 MHz
Div 128 = 131 kHz Div 128 = 164 kHz
Div 2 = 8.39 MHz
Div 4 = 4.19 MHz
Div 8 = 2.10 MHz
Div 32 = 524 kHz
Div 64 = 262 kHz
16.78 MHz
PCLK
Prescaler Tap
Using 16.78-MHz/20.97-MHz System Clocks
Freescale Semiconductor, Inc.
Div 2 = 10.5 MHz
Div 4 = 5.25 MHz
Div 8 = 2.62 MHz
Div 32 = 655 kHz
Div 64 = 328 kHz
For More Information On This Product,
Table 7-3 PWM Frequency Ranges
20.97 MHz
PCLK
GENERAL-PURPOSE TIMER
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16.78 MHz
PCLK/256
32.8 kHz
16.4 kHz
8.19 kHz
4.09 kHz
2.05 kHz
1.02 kHz
512 Hz
SFA/B = 0
20.97 MHz
PCLK/256
20.5 kHz
10.2 kHz
5.15 kHz
2.56 kHz
1.28 kHz
641 Hz
41 kHz
PCLK/32768
16.78 MHz
64.0 Hz
32.0 Hz
16.0 Hz
256 Hz
128 Hz
8.0 Hz
4.0 Hz
SFA/B = 1
20.97 MHz
PCLK/32768
80.0 Hz
40.0 Hz
20.0 Hz
10.0 Hz
320 Hz
160 Hz
5.0 Hz
7-17
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