
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 FDC resumes operation as though it was never in powerdown.  Besides 
activating the PCI_RESET# pin or one of the software reset bits in the DOR or DSR, the following register accesses 
will wake up the part: 
1. Enabling any one of the motor enable bits in the DOR register (reading the DOR does not awaken the part). 
2. A read from the MSR register. 
3. A read or write to the Data register. 
Once awake, the FDC will reinitiate the auto powerdown  timer  for  10 ms.   The   part will powerdown again when all 
the powerdown  conditions are satisfied. 
SMSC DS – LPC47M192 
Page 99 
Rev. 03/30/05 
DATASHEET 
Register Behavior 
Table 46illustrates the AT and PS/2 (including Model 30) configuration registers available and the type of access 
permitted.  In order to maintain software transparency, access to all the registers must be maintained. As Table 46 
shows, two sets of registers are distinguished based on whether their access results in the part remaining in 
powerdown state or exiting it. 
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 will revert back to its low power mode when the access has been 
completed. 
Pin Behavior 
The LPC47M192 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 LPC47M192 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 46 - PC/AT and PS/2 Available Registers 
AVAILABLE REGISTERS 
PC-AT 
PS/2 (MODEL 30) 
BASE + 
ADDRESS 
ACCESS PERMITTED 
Access to these registers DOES NOT wake up the part 
---- 
---- 
DOR (1) 
--- 
DSR (1) 
--- 
DIR 
CCR 
Access to these registers wakes up the part 
MSR 
Data 
00H 
01H 
02H 
03H 
04H 
06H 
07H 
07H 
SRA 
SRB 
DOR (1) 
--- 
DSR (1) 
--- 
DIR 
CCR 
R 
R 
R/W 
--- 
W 
--- 
R 
W 
04H 
05H 
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 47 gives the state of the interface pins in the powerdown state.  Pins unaffected by the powerdown are labeled 
“Unchanged.”