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.
back to its low power mode when the access
has been completed.
Pin 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.
Register Behavior
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
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.
part awakens.
Accessing the part during
powerdown may cause an increase in the power
consumption by the part. The part will revert
110
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