AUTO POWER MANAGEMENT
Power management capabilities are provided for
DSR From Powerdown
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.
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.
FDC Power Management
Direct power management is controlled by
CR22. Refer to CR22 for more information.
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.
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:
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
RESET pin or one of the software reset bits in
the DOR or DSR, the following register
accesses will wake up the part:
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.
1. Enabling any one of the motor enable bits
in the DOR register (reading the DOR does
not awaken the part).
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.
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.
Disabling the auto powerdown mode cancels the
timer and holds the FDC block out of auto
powerdown.
103
SMSC [ SMSC CORPORATION ]
