MC68HC908RF2MFA Freescale Semiconductor, MC68HC908RF2MFA Datasheet - Page 76

• Manufacturer Part Number: MC68HC908RF2MFA
• Description: IC MCU 2K FLASH 4MHZ 32-LQFP
• Manufacturer: Freescale Semiconductor
• Series: HC08r

Specifications of MC68HC908RF2MFA

• Core Processor: HC08
• Core Size: 8-Bit
• Speed: 4MHz
• Peripherals: LVD, POR, PWM, RF Mod
• Number Of I /o: 12
• Program Memory Size: 2KB (2K x 8)
• Program Memory Type: FLASH
• Ram Size: 128 x 8
• Voltage - Supply (vcc/vdd): 1.8 V ~ 3.6 V
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 32-LQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Eeprom Size: -
• Data Converters: -
• Connectivity: -

Internal Clock Generator Module (ICG)
6.4 Usage Notes
6.4.1 Switching Clock Sources
Data Sheet
76
The switch automatically selects ICLK during reset. When the clock monitor is on
(CMON is set) and it determines one of the clock sources is inactive (as indicated
by the IOFF or EOFF signals), the circuit is forced to select the active clock. There
are no clocks for the inactive side of the synchronizer to properly operate, so that
side is forced deselected. However, the active side will not be selected until one to
two clock cycles after the IOFF or EOFF signal transitions.
The ICG has several features which can provide protection to the microcontroller if
properly used. There are other features which can greatly simplify usage of the ICG
if certain techniques are employed. This section will describe several possible
ways to use the ICG and its features. These techniques are not the only ways to
use the ICG, and may not be optimum for all environments. In any case, these
techniques should be used only as a template, and the user should modify them
according to the application’s requirements.
These notes include:
Switching from one clock source to another requires both clock sources to be
enabled and stable. A simple flow requires:
The key point to remember in this flow is that the clock source cannot be switched
(CS cannot be written) unless the desired clock is on and stable.
A short assembly code example of how to employ this flow is shown in
This code is for illustrative purposes only and does not represent valid syntax for
any particular assembler.
1. Enable desired clock source
2. Wait for it to become stable
3. Switch clocks
4. Disable previous clock source
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Switching clock sources
Enabling the clock monitor
Using clock monitor interrupts
Quantization error in DCO output
Switching internal clock frequencies
Nominal frequency settling time
Improving frequency settling time
Trimming frequency
Freescale Semiconductor, Inc.
For More Information On This Product,
Internal Clock Generator Module (ICG)
Go to: www.freescale.com
MC68HC908RF2 — Rev. 4.0
Figure
MOTOROLA
6-7.