Intel 80C186XL, User Manual

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5-11
CLOCK GENERATION AND POWER MANAGEMENT
5.2.1 Power-Save Mode
Power-Save mode is a means for reducing operating current. Power-Save mode enables a pro-
grammable clock divider in the clock generation circuit.
NOTE
Power-Save mode can be used to stretch bus cycles as an alternative to wait
states.
Possible clock divisor settings are 1 (undivided), 4, 8 and 16. The divided frequency feeds the
core, the integrated peripherals and CLKOUT. The processor operates at the divided clock rate
exactly as if the crystal or external oscillator frequency were lower by the same amount. Since
the processor is static, a lower limit clock frequency does not apply. It may be necessary to repro-
gram integrated peripherals such as the Timer Counter Unit and the Refresh Control Unit to com-
pensate for the overall reduced clock rate.
5.2.1.1 Entering Power-Save Mode
The Power-Save Register (Figure 5-9) controls Power-Save mode operation. The lower two bits
select the divisor. When program execution sets the PSEN bit, the processor enters Power-Save
mode. The internal clock frequency changes at the falling edge of T3 of the write to the Power-
Save Register. CLKOUT changes simultaneously and does not glitch. Figure 5-10 illustrates the
change at CLKOUT.