POWER MANAGEMENT
Power management capabilities are provided for
the part is awakened from DSR powerdown, the
auto powerdown will once again become effective.
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.
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.
FDC POWER MANAGEMENT
Direct power management is controlled by CR22.
Refer to CR22 for more information.
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
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:
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.
4. The Auto powerdown timer (10msec) must
have timed out.
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.
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.
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.
Register Behavior
Table 44 illustrates the AT and PS/2 (including
Model 30) configuration registers available and the
type of access permitted. In order to maintain
software transparency, access to all the registers
must be maintained. As Table 44 shows, two sets
of registers are distinguished based on whether
their access results in the part remaining in
powerdown state or exiting it.
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
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