Once awake, the FDC37C669 will reinitiate the auto
powerdown timer for 10 ms. The part will powerdown
again when all the powerdown conditions are satisfied.
will revert back to its low power mode when the
access has been completed.
Pin Behavior
Register Behavior
The FDC37C669 is specifically designed for portable PC
systems in which power conservation is a primary
concern. This makes the behavior of the pins during
powerdown very important.
Table 43 reiterates the AT and PS/2 (including modes 30)
configuration registers available. It also shows the type of
access permitted.
In order to maintain software
transparency, access to all the registers must be
maintained. As Table 43 shows, two sets of registers are
distinguished based on whether their access results in the
part remaining in powerdown state or exiting it.
The pins of the FDC37C669 can be divided into two
major categories: system interface and floppy disk drive
interface. The floppy disk drive pins are disabled so that
no power will be drawn through the part as a result of any
voltage applied to the pin within the part's power supply
range. Most of the system interface pins are left active to
monitor system accesses that may wake up the part.
Access to all other registers is possible without
awakening the part. These registers can be accessed
during powerdown without changing the status of the part.
A read from these registers will reflect the true status as
shown in the register description in the FDC description.
A write to the part will result in the part retaining the data
and subsequently reflecting it when the part awakens.
Accessing the part during powerdown may cause an
increase in the power consumption by the part. The part
System Interface Pins
Table 44 gives the state of the system interface pins in
the powerdown state.
Pins unaffected by
the
powerdown are labeled "Unchanged". Input pins are
"Disabled" to prevent them from causing currents internal
to the FDC37C669 when they have indeterminate input
values.
109
SMSC [ SMSC CORPORATION ]
