SMC Networks SMC91C95 manual General Description, Overview

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

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