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 will revert back to its
low power mode when the access has been completed.
Pin Behavior
The LPC47B27x is specifically designed for systems in which power conservation is a primary concern.
This makes the behavior of the pins during powerdown very important.
The pins of the LPC47B27x 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.
Table 48 - PC/AT and PS/2 Available Registers
AVAILABLE REGISTERS
BASE + ADDRESS
PC-AT
PS/2 (MODEL 30)
ACCESS PERMITTED
Access to these registers DOES NOT wake up the part
00H
01H
02H
03H
04H
06H
07H
07H
----
----
SRA
SRB
DOR (1)
---
DSR (1)
---
DIR
CCR
R
R
DOR (1)
---
R/W
---
W
DSR (1)
---
---
R
W
DIR
CCR
Access to these registers wakes up the part
04H
05H
MSR
Data
MSR
Data
R
R/W
Note 1: Writing to the DOR or DSR does not wake up the part, however, writing any of the motor enable
bits or doing a software reset (via DOR or DSR reset bits) will wake up the part.
System Interface Pins
Table 49 gives the state of the interface pins in the powerdown state. Pins unaffected by the powerdown
are labeled "Unchanged".
Table 49 – State of System Pins in Auto Powerdown
SYSTEM PINS
LAD[3:0]
STATE IN AUTO POWERDOWN
Unchanged
nLDRQ
Unchanged
nLPCPD
Unchanged
nLFRAME
nPCI_RESET
PCI_CLK
Unchanged
Unchanged
Unchanged
SER_IRQ
Unchanged
FDD Interface Pins
All pins in the FDD interface which can be connected directly to the floppy disk drive itself are either
DISABLED or TRISTATED.
Pins used for local logic control or part programming are unaffected. Table 50 depicts the state of the
floppy disk drive interface pins in the powerdown state.
Table 50 - State of Floppy Disk Drive Interface Pins in Powerdown
FDD PINS
STATE IN AUTO POWERDOWN
INPUT PINS
Input
nRDATA
nWRTPRT
Input
SMSC LPC47B27x
- 95 -
Rev. 08-10-04
DATASHEET
SMSC [ SMSC CORPORATION ]
