Revision 1.1
69
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G
SuperI/O Module
(Continued)
Write accesses to unimplemented registers (i.e., accessing
the Data register while the Index register points to a non-
existing register or the LDN is higher than 08h), are ignored
and a read returns 00h on all addresses except for 74h and
75h (DMA configuration registers) which returns 04h (indi-
cating no DMA channel is active). The configuration regis-
ters are accessible immediately after reset.
4.3.3
The device has four reset types:
Default Configuration Setup
Software Reset
This reset is generated by bit 1 of the SIOCF1 register,
which resets all logical devices. A software reset also
resets most bits in the SIO Configuration and Control regis-
ters (see Section 4.4.1 on page 73 for the bits not affected).
This reset does not affect register bits that are locked for
write access.
Hardware Reset
This reset is activated by the system reset signal. This
resets all logical devices, with the exception of the RTC and
the SWC, and all SIO Configuration and Control registers,
with the exception of the SIOCF2 register. It also resets all
SIO Control and Configuration registers, except for those
that are battery-backed.
V
PP
Power-Up Reset
This reset is activated when either V
SB
or V
BAT
is powered
on after both have been off. V
PP
is an internal voltage
which is a combination of V
SB
and V
BAT
. V
PP
is taken from
V
SB
if V
SB
is greater than the minimum (Min) value defined
in Section 7.1.3 "Operating Conditions" on page 281; oth-
erwise, V
BAT
is used as the V
PP
source. This reset resets
all registers whose values are retained by V
PP
.
V
SB
Power-Up Reset
This is an internally generated reset that resets the SWC,
excluding those SWC registers whose values are retained
by V
PP
. This reset is activated after V
SB
is powered up.
The SIO module wakes up with the default setup, as fol-
lows:
When a hardware reset occurs:
— The configuration base address is 2Eh, 15Ch or
None, according to the IO_SIOCFG_IN bit values, as
shown in Table 4-1 on page 68.
— All Logical devices are disabled, with the exception of
the RTC and the SWC, which remains functional but
whose registers cannot be accessed.
When either a hardware or a software reset occurs:
— The legacy devices are assigned with their legacy
system resource allocation.
— The National proprietary functions are not assigned
with any default resources and the default values of
their base addresses are all 00h.
4.3.4
A full 16-bit address decoding is applied when accessing
the configuration I/O space, as well as the registers of the
functional blocks. However, the number of configurable bits in
the base address registers vary for each device.
Address Decoding
The lower 1, 2, 3 or 4 address bits are decoded within the
functional block to determine the offset of the accessed
register, within the device’s I/O range of 2, 4, 8 or 16 bytes,
respectively. The rest of the bits are matched with the base
address register to decode the entire I/O range allocated to
the device. Therefore the lower bits of the base address
register are forced to 0 (RO), and the base address is
forced to be 2, 4, 8 or 16 byte aligned, according to the size
of the I/O range.
The base address of the RTC, Serial Port, and the Infrared
Communication Port are limited to the I/O address range of
00h to 7Fxh only (bits [15:11] are forced to 0).The
addresses of the non-legacy devices are configurable
within the full 16-bit address range (up to FFFxh).
In some special cases, other address bits are used for
internal decoding. For more details, please see the detailed
description of the base address register for each specific
logical device.