lan91c95 Standard Microsystems Corp., lan91c95 Datasheet - Page 50

• Manufacturer Part Number: lan91c95
• Description: Isa/pcmcia Full Duplex Single-chip Ethernet And Modem Controller With Ram
• Manufacturer: Standard Microsystems Corp.

8032h - Modem I/O Size Register
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
LAN91C95 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
LAN91C95. The LAN91C95 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 LAN91C95 will tri-
0
0
0
Modem I/O Size Mask
0
50
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 LAN91C95,
LAN91C92, 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 LAN91C95 banks, while Banks 4
and 5 allow access to the multifunction registers in
ISA mode.
0
1
1
1