AT&T 3B2/300 Technical Reference Manual page 489

FUNCTIONAL D E S C R I P T I O N - - - - - - - - - - - - - - - - - - - - - - - - - -
Local RAM
The STARLAN Interface card contains 32K bytes of Static Random Access Memory (SRAM)
configured as 16K by 16 bits. The DRAM is accessed via the Low Memory Chip Select (LCSO) from
80186 Microprocessor and address bits 12-00. Note that 256K bytes of RAM address space is
reserved. The 32K bytes of RAM is used for intermediate data storage of the data being transmitted
to/received from the network.
Local ROM
Firmware for the 80186 Microprocessor is stored in the ROM. The STARLAN Interface card ROM
contains 16K bytes configured as 8K by 16 bits. The ROM is accessed via the Upper Memory Chip
Select (UCS[O]) and address bits 14-00.
Network Interface
The AT&T STARLAN is an Ethernet compatible, local area network. Data is transferred over the
network by attaching a destination identification to the data to be transferred. The nisend command is
used to attach a destination code and file name to the data to be transferred. The STARLAN Interface
Card firmware handles the transfer of the data between the 3B2 computer main memory and the
Network Interface local RAM. The data to be transferred is divided into packets of 1024 bytes for
transfer over the network. The Ethernet Controller autonomously reads the data from local RAM,
converts the data to serial stream, and transmits the stream over the network. If collisions are detected,
the information packet is retransmitted automatically. The receiving system acknowledges the receipt of
the data.
Ethernet Controller Circuit
The Network Interface is a 82586 Ethernet Controller that manages the process of transmitting and
receiving data over the network. The primary functions of the controller are to do the following:
• Decode the serial data
• Check for data integrity
• Convert serial data into parallel data format
• Store parallel data in the local RAM
• Save and report networking errors for the node.
The Network Access Unit Serial Interface provides the connection between the 82586 LAN
Coprocessor and the transmission media. The interface consists of the following signals.
Receive Pair
A differential signal that is active when any data is received.
Transmit Pair
A differential signal that is active when any data is transmitted.
Collision Presence Pair
A differential signal that is active while a collision is in progress.
Connectors are provided to support both daisy-chained and star connections (Jl and J2). A
connector (J3) is also provided for a telephone link to an AT&T Premises Distribution System.
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