90
8032h - Modem I/O Size Register
Modem I/O Size Mask
00000111
The I/O Size Register holds a bit mask used to
specify the number of address lines decoded by
the Modem function. Each bit in the register
represents an I/O address line. A value of one
means that the SMC91C95 will not decode the
corresponding address line for the Modem
function, a value of zero means that the address
line will be decoded. If a bit in the register is set to
one, all bits of lesser significance in the register
must also be set to one.
This register defaults to 7h, that is A0, A1 and A2
are not decoded resulting in 8 address locations for
the modem function.
Modem I/O Space: Address determined by
Modem I/O Base Registers
The Modem I/O space is external to the
SMC91C95. The SMC91C95 decodes the address
bus ( A15 through A3) via a internal comparator
and generates nMCS for I/O cycles that decode to
the Modem area as defined by the Modem I/O
Base Registers. The I/O address space consists
of eight (8) 8-bit locations. The
SMC91C95 will tri-state the data bus during
Modem I/O space accesses. In ISA mode, nMCS
is disabled (1). No address decodeing for the
modem will be done.
Ethernet I/O Space: Address determined by
Ethernet I/O Base Registers
The Ethernet I/O space consists of sixteen
locations whose base address is determined in
PCMCIA mode by the Ethernet I/O Base
Registers, and in ISA mode by the default value of
the Base Register (either reset or serial EEPROM
default in ISA mode only).
The Ethernet I/O space can be configured as an 8
or 16 bit space, and is similar to the SMC91C95,
SMC91C92, etc. I/O space. To limit the I/O space
requirements to 16 locations, the registers are split
into six banks. The last word of the I/O area is
shared by all banks and can be used to change the
bank in use. Banks 0 through 3 functionally
correspond to the SMC91C95 banks, while Banks
4 and 5 allow access to the multifunction registers
in ISA mode.