Infineon XC800 Series, Руководство пользователя

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AP08056
Power Saving Features
Operating on a Lower Frequency Clock Mode
Application Note 21 V1.0, 2006-12
PLL_CON &= 0xF7;//Deselect VCO bypass mode
//... device is running in PLL Mode
6.2 Device Clock in Prescaler Mode
In this mode, the system clock is derived from the oscillator clock divided by the P and
K factor:
The oscillator frequency is close to it designated frequency (10 MHz for XC866 and 9.6
MHz for XC886/888.) after it has been trimmed by the factory. Below are some results
showing the current consumption by the four devices operating in prescaler mode.
The current consumption is much lower than the device operating in slow-down mode in
Section 3.2 . The combination of slow-down and idle mode may not be as efficient as
slow-down alone at low frequencies. For example for the XC888 device, it will draw 3.35
mA of current for the combined slow-down and idle mode compared to 2.89 mA for slow-
down mode alone when bitfield CMCON.CLKREL = 1111
B
.
6.2.1 Software Example for Prescaler Mode
The system clock can operate in prescaler mode by setting the bit PLL_CON.VCOBYP.
The following example shows how the prescaler mode is selected.
SCU_PAGE = 0x01;//Open SCU page 1
PLL_CON |= 0x08;//Select VCO Bypass Mode
PLL mode can be restored from prescaler mode simply by clearing the bit
PLL_CON.VCOBYP.
PLL_CON &= 0xF7;//Deselect VCO bypass mode
Table 13 Current consumption in prescaler mode
XC866-1FR XC866-4-FR XC886 XC888
Internal oscillator
frequency (f
osc
)
10.5 MHz 9.98 MHz 9.75 MHz 9.65 MHz
System frequency
(f
sys
)
1)
1) f
sys
= 1/(P*K)*f
osc
where P = 1 and K = 2
5.25 MHz 4.99 MHz 4.875 MHz 4.825 MHz
Active mode current 3.13 mA 3.53 mA 3.85 mA 3.84 mA
Slow-down mode
current
2)
2) CLKREL = 1011
B
for XC866 and CLKREL = 1111
B
for XC886/888
2.28 mA 2.70 mA 2.89 mA 2.89 mA
f
SYS
1
P K
⋅
------------ f
OSC
⋅
=