参数资料
型号: SPMC16V1CPU20
厂商: MOTOROLA INC
元件分类: 微控制器/微处理器
英文描述: 16-BIT, MROM, 20.97 MHz, MICROCONTROLLER, PQFP100
封装: TQFP-100
文件页数: 48/128页
文件大小: 571K
代理商: SPMC16V1CPU20
MOTOROLA
MC68HC16V1
26
MC68HC16V1TS/D
3.3.5 Avoiding Frequency Overshoot
In slow and fast reference modes, changing the W and Y fields in the SYNCR to increase the operating
frequency can result in frequency overshoot. This overshoot can be avoided by using the following pro-
cedure:
1.
Determine the values for the W and Y fields which will result in the desired frequency when the
X bit is set.
2.
With the X bit cleared, write these values for the W and Y fields to SYNCR.
3.
After the VCO locks, set the X bit in the SYNCR. This changes the clock frequency to the de-
sired frequency.
For example, use the following procedure in fast reference mode (PCON2 = 1) to change the clock fre-
quency from 8.388 MHz to 20.972 MHz after reset using a 4.194 MHz crystal:
1.
Determine the values for the W and Y fields: W = %100, Y = %000
2.
Write the values to SYNCR: W = %100, Y = %000
3.
Wait for the SYNCR SLOCK bit to set. When SLOCK = 1, the VCO has locked the new
frequency, now 10.486 MHz.
4.
Set the SYNCR X bit to one. This removes a divider from the synthesizer output path, effectively
doubling the clock frequency from 10.486 MHz to 20.972 MHz.
3.4 System Protection
The system protection block incorporates several monitoring and timing functions. System protection
block features include:
Software watchdog timer
Real-time clock
Prescaler
Bus monitor
Spurious interrupt monitor
Halt monitor
These functions have been made integral to the microcontroller to reduce the number of external com-
ponents in a complete control system.
Figure 8 shows the system protection block.
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