37C957FR Datasheet, PDF (26/328 Pages) SMSC Corporation – ULTRA I/O CONTROLLER FOR PORTABLE APPLICATIONS

AUTO POWER MANAGEMENT
Auto Power management capabilities are provided for the following logical devices: Floppy Disk,
UART 1, UART 2 and the Parallel Port. For each logical device, two types of power management are
provided; direct powerdown and auto powerdown.
System Power Management
See the “8051 System Power Management” section for details.
FDC Power Management
Direct power management is controlled through Global Configuration Register 22 (CR22). Refer to
CR22 in the Configuration section for more information.
Auto Power Management is enabled through bit-0 of CR23. When set, this bit allows FDC to enter
powerdown when all of the following conditions have been met:
1. The motor enable pins of the FDC’s DOR register are inactive (zero).
2. The part must be idle; the MSR register =80h and the FDC’s INTerrupt = 0 (INT may be high
even if MSR = 80H due to polling interrupts).
3. The head unload timer must have expired.
4. The Auto powerdown timer (10msec) must have timed out.
An internal timer is initiated as soon as the auto powerdown command is enabled. The part is then
powered down when all the conditions are met.
Disabling the auto powerdown mode cancels the timer and holds the FDC block out of auto
powerdown.
DSR From Powerdown
Bit-6 of the FDC’s DSR register is another FDC powerdown bit. If DSR powerdown is used when the
part is in auto powerdown, the DSR powerdown will override the auto powerdown. However, when
the part is awakened from DSR powerdown, the auto powerdown will once again become effective.
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