Register Behavior
Pin Behavior
Table 47 reiterates the AT and PS/2 (including
Model 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 47 shows, two sets of registers are
distinguished based on whether their access
results in the part remaining in powerdown state
or exiting it.
The FDC37C93xFR 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.
The pins of the FDC37C93xFR 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
part awakens.
Accessing the part during
Table 48 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 FDC37C93xFR
when they have indeterminate input values.
powerdown may cause an increase in the power
consumption by the part. The part will revert
back to its low power mode when the access
has been completed.
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SMSC [ SMSC CORPORATION ]
