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"--PR_I_NC_I_P_LE_S_O_F_O_P_ER_A_T_IO_N
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INRODUCTION
This section has a description of the HP 30240A OfficeShare LAN/3000 Link, Local Area Network
Interface Controller (LANIC). The description gives the principles of operation.
FUNCTIONAL DESCRIPTION
The HP 30240A OfficeShare LAN/3000 link is an implementation of the IEEE 802.2 and IEEE 802.3
Local Area Network (LAN) standards and is used to allow HP 3000 computer systems to communicate
with other HP 3000's over a Local Area Network (LAN). The IEEE 802.2 Local Area Network standard
defines a logical link control protocol, and IEEE 802.3 Local Area Network standard defines a bus
utilizing CSMA/CD (Carrier Sense Multiple Access/Collision Detect) as the access method.
The LAN/3000 link functions as an intelligent Direct Memory Access (DMA) channel which
communicates with the host system via the system backplane. Local intelligent control is provided by a
microprocessor and firmware on the LAN Interface Controller (LANIC).
The LAN/3000 link consists of a LAN Interface Controller (LANIC), and a Thin Medium Attachment
Unit (ThinMAU).
The ThinMAU attaches to a coaxial cable which connects the various computer
systems together on the Local Area Network; and the LANIC provides the interface between the LAN
and the computer system.
LAN INTERFACE CONTROL.LER (lANIC)
The LANIC is an intelligent DMA channel which communicates with the host system via the system
backplane. On the network end of the LANIC, the AUI carries bit-serial data and control information to
and from the MAU, which attaches directly to the network coaxial cable. A functional block diagram of
the LANIC is shown in figure 3-1.
Host to LANIC Communication.
The host communicates with LANIC through channel registers and data structures stored in system
memory. Basic channel communication registers provide for channel identification, interrupt control, and
diagnostics. Of primary importance are the Control Register (CR) and Status Register (SR), which provide
for the input and output of control and status information. Link-level commands and status are passed
via two queue structures stored in system memory shared by the LANIC and the host.
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3-1
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