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GENERAL DESCRIPTION
The SMC91C95 is a VLSI Ethernet Controller
that combines ISA and PCMCIA interfaces, as
well as an interface to a companion modem
chip set, in one chip. The SMC91C95
integrates all the MAC and physical layer
functions as well as the packet RAM needed to
implement a high performance 10BASE-T
(twisted pair) node. For 10BASE5 (thick coax),
10BASE2 (thin coax), and 10BASE-F (fiber)
implementations, the SMC91C95 interfaces to
external transceivers via its AUI port. Only one
additional IC is required on most applications.
The SMC91C95 occupies 16 I/O locations and
no memory space except for PCMCIA attribute
memory space. The same I/O space is used for
both ISA and PCMCIA operations. The
SMC91C95 can directly interface the ISA and
PCMCIA buses and deliver no wait state
operation. Its shared memory is sequentially
accessed with 40ns access times to any of its
registers, including its packet memory. No
DMA services are used by the SMC91C95;
virtually decoupling network traffic from local or
system bus utilization. For packet memory
management, the SMC91C95 integrates a
unique hardware Memory Management Unit
(MMU) with enhanced performance and
decreased software overhead when compared
to ring buffer and linked list architectures. The
SMC91C95 is portable to different CPU and bus
platforms due to its flexible bus interface, flat
memory structure (no pointers), and its loosely
coupled buffered architecture (not sensitive to
latency).
The SMC91C95 interfaces directly with
Rockwell International L39/C39 controller-based
modems and Lucent Technologies’
HSM288xCF modem.
OVERVIEW
A unique architecture allows the SMC91C95 to
combine high performance, flexibility, high
integration and simple software interface.
The SMC91C95 incorporates the SMC91C92/4
functionality for ISA environments with several
new features, as well as a PCMCIA interface
and attribute registers that comply with the
PCMCIA Multi-Function specification. Mode
selection between ISA and PCMCIA is static
and is done only once at the end of power on
reset. The SMC91C95 consists of the same
logical I/O register structure in ISA and
PCMCIA modes. However, some of the signals
used to access the PCMCIA differ from the ISA
mode. Additional registers exist in the PCMCIA
attribute space. The ROM memory space only
exists in ISA mode and the attribute space only
exists in PCMCIA mode.
I/O decoders are included in the SMC91C95’s
PCMCIA interface, with independent decoders
for the LAN and for the modem functions.
These decoders are used whenever the
SMC91C95 is used as a multi-function card,
and they can be bypassed when only one
function is enabled. The SMC91C95 also
merges the LAN’s internal interrupt source with
the external modem interrupt connected to the
SMC91C95.
The MMU (Memory Management Unit)
architecture used by the SMC91C95 combines
the simplicity and low overhead of fixed areas
with the flexibility of linked lists providing
improved performance over other methods.
The SMC91C95 is designed to support full
duplex switched Ethernet where transmit and