MC68HC908KX2CP Freescale Semiconductor, MC68HC908KX2CP Datasheet - Page 70

• Manufacturer Part Number: MC68HC908KX2CP
• Description: IC MCU 2K FLASH 8MHZ SCI 16-DIP
• Manufacturer: Freescale Semiconductor
• Series: HC08r

Specifications of MC68HC908KX2CP

• Core Processor: HC08
• Core Size: 8-Bit
• Speed: 8MHz
• Connectivity: SCI
• Peripherals: LVD, POR, PWM
• Number Of I /o: 13
• Program Memory Size: 2KB (2K x 8)
• Program Memory Type: FLASH
• Ram Size: 192 x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 4x8b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 16-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Eeprom Size: -

Internal Clock Generator Module (ICG)
7.3.2.1 Digitally Controlled Oscillator
The digitally controlled oscillator (DCO) is an inaccurate oscillator which generates the internal clock
(ICLK). The clock period of ICLK is dependent on the digital loop filter outputs (DSTG[7:0] and DDIV[3:0]).
Because there is only a limited number of bits in DDIV and DSTG, the precision of the output (ICLK) is
restricted to a precision of approximately ±0.202% to ±0.368% when measured over several cycles (of
the desired frequency). Additionally, since the propagation delays of the devices used in the DCO ring
oscillator are a measurable fraction of the bus clock period, reaching the long-term precision may require
alternately running faster and slower than desired, making the worst case cycle-to-cycle frequency
variation ±6.45% to ±11.8% (of the desired frequency). The valid values of DDIV:DSTG range from $000
to $9FF. For more information on the quantization error in the DCO, see
Output.
7.3.2.2 Modulo "N" Divider
The modulo "N" divider creates the low frequency base clock (IBASE) by dividing the internal clock (ICLK)
by the ICG multiplier factor (N), contained in the ICG multiplier register (ICGMR). When N is programmed
to a $01 or $00, the divider is disabled and ICLK is passed through to IBASE undivided. When the ICG is
stable, the frequency of IBASE will be equal to the nominal frequency (f
7.3.2.3 Frequency Comparator
The frequency comparator effectively compares the low frequency base clock (IBASE) to a nominal
frequency, f
capacitor with a current reference for a period dependent on IBASE. This voltage is compared to a voltage
70
VOLTAGE AND
REFERENCES
ICGEN
CURRENT
NOM
. First, the frequency comparator converts IBASE to a voltage by charging a known
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 Data Sheet, Rev. 2.1
NAME
NAME
Figure 7-2. Internal Clock Generator Block Diagram
CONFIG (OR MOR) REGISTER BIT
TOP LEVEL SIGNAL
- -
++
COMPARATOR
LOOP FILTER
FREQUENCY
CLOCK GEN
TRIM[7:0]
DIGITAL
NAME
NAME
CONTROLLED
OSCILLATOR
DIGITALLY
MODULO
DIVIDER
N[6:0]
"N"
NOM
7.4.4 Quantization Error in DCO
REGISTER BIT
MODULE SIGNAL
) of 307.2 kHz ± 25%.
Freescale Semiconductor
DSTG[7:0]
DDIV[3:0]
FICGS
IBASE
ICLK