
117
Register Behavior
Table 41 illustrates 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 41 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 LPC47B34x 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 LPC47B34x 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 41 - 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.