6.8 Power Management
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.
Note: For additional power management capabilities see the following sections:
LPC Interface, subsection 6.3.2 Power Management on page 26.
Real Time Clock, subsection 6.9.9 Power Management on page 104.
8042 Keyboard Controller Description, subsection 6.11.3 Keyboard Power Management on page 110
ACPI/PME/SMI Features on page 147
6.8.1 FDC POWER MANAGEMENT
Direct power management is controlled by CR22. Refer to CR22 for more information.
Auto Power Management is enabled by CR23-B0. When set, this bit allows FDC to enter powerdown when all of the
following conditions have been met:
1. The motor enable pins of register 3F2H are inactive (zero).
2. The part must be idle; MSR=80H and INT = 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.
Note: At least 8us delay should be added when exiting FDC Auto Powerdown mode. If the operating environment is
such that this delay cannot be guaranteed, the auto powerdown mode should not be used and Direct powerdown
mode should be used instead. The Direct powerdown mode requires at least 8us delay at 250K bits/sec
configuration and 4us delay at 500K bits/sec. The delay should be added so that the internal microcontroller can
prepare itself to accept commands.
DSR From Powerdown
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.
Wake Up From Auto Powerdown
If the part enters the powerdown state through the auto powerdown mode, then the part can be awakened by reset or by
appropriate access to certain registers.
If a hardware or software reset is used then the part will go through the normal reset sequence. If the access is through
the selected registers, then the FDC resumes operation as though it was never in powerdown. Besides activating the
PCI_RESET# pin or one of the software reset bits in the DOR or DSR, the following register accesses will wake up the
part:
1. Enabling any one of the motor enable bits in the DOR register (reading the DOR does not awaken the part).
2. A read from the MSR register.
3. A read or write to the Data register.
Once awake, the FDC will reinitiate the auto powerdown timer for 10 ms. The part will powerdown again when all the
powerdown conditions are satisfied.
Register Behavior
SMSC DS – LPC47S45x
Page 94 of 259
Rev. 07/09/2001
DATASHEET
SMSC [ SMSC CORPORATION ]
