FDC37C78-HT datasheet(58/82 Pages) MICROCHIP

58 / 82 page

AUTO POWER MANAGEMENT

Power management capabilities are provided for

the floppy disk. Two types of power management

are

provided;

direct

powerdown

and

auto

powerdown.

Direct powerdown is controlled by the powerdown

bit in the configuration registers. Auto Powerdown

can be enabled by setting the Auto Powerdown

Enable bit in the configluation registers.

FDC Power Management

Direct power management is controlled by bit 3 of

Configuration Register 0(CR0).

Refer to CR0 bit

3 for more information.

Auto Power Management is enabled by CR7 bit 7.

When set, this bit allows FDC to enter powerdown

when all of the following conditions have been met:

The motor enable pins of register DOR are

inactive (zero).

The part must be idle; MSR=80H and INT = 0

(INT may be high even if MSR = 80H due to

polling interrupts).

The internal head unload timer must have

expired.

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.

During the countdown of the powerdown

timer, any operation of read MSR or read/write

data (FIFO) will reinitiate the timer.

Disabling the auto powerdown mode cancels the

timer and holds the FDC37C78 out

of auto

powerdown.

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 FDC37C78 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:

Enabling any one of the motor enable bits in

the DOR register (reading the DOR does not

awaken the part).

A read from the MSR register.

A read or write to the Data register.

FDC37C78-HT Datasheet(PDF) 58 Page - Microchip Technology

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