_Ge_N_E_R_A_L_In_F_O_R_M_A_T_Io_N; General Description - HP 30242 Installation And Service Manual

_GE_N_E_R_A_L_IN_F_O_R_M_A_T_IO_N
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This manual presents installation and service instructions for the HP 30242A LAN/3000 Link Local Area
Network Interface Controller. This section contains general information covering the HP 30242A
LAN/3000 link product, and includes a description and specifications.
GENERAL DESCRIPTION
The HP 30242A LAN/3000 link is an implementation of the IEEE 802.2 and IEEE 802.3 Local Area
Network (LAN) standards and is used in HP 3000 computer systems. The HP 30242A allows the !:lP
3000 to communicate with other HP 3000s over an IEEE 802.3, O. 4-inch baseband Local Area Network
(LAN).
The IEEE 802.3 Local Area Networks (LANs) consist of three major elements: a coaxial cable transmission
medium, units to access this medium (Medium Attachment Units, or MAUs), and controllers. For the
HP 30242A, the controller is the Local Area Network Interface Controller (LANIC).
A fitting, called a
tap,
pierces the coaxial cable and provides a connection from the cable to the Medium
Attachment Unit (MAU). An Attachment Unit Interface (AUI) cable connects the MAU to the LAN
Interface Controller (LANIC). The LANIC, in addition to controlling the other LAN elements, functions
as the interface from the Local Area Network to the computer system. A typical Local Area Network is
shown in figure 1-1. Each host computer system, including LANIC, AUI, tap, and MAU is called a
node
on the Local Area Network. The LANIC, AUI, tap, and MAU are all part of the HP 30242A LAN/3000
link.
The HP 30242A LAN/3000 link is available for use with the HP 3000 Series 39, 40, and 42; and the HP
3000 Series 44, 48 64, and 68. The LANIC, MAU, and AUI cable are the same for all HP 3000 Series;
however, two different LANIC cables are offered (see the paragraph "Equipment Supplied").
The LAN/3000 link functions as an intelligent Direct Memory Access (DMA) channel which
communicates with the host system via the system
I/O
backplane. Local intelligent control is provided by
a microprocessor and firmware on the LAN Interface Controller (LANIC). An 8-bit Z-80B
microprocessor (MPU) on the LANIC handles all the LAN/3000-to-host communication and performs
many link-level operations independently of the host. A type 82586 Local Communications Controller
(LCC) on the LANIC performs high-speed serial operations, packet address checking, network contention
control, packet formatting, and Cyclic Redundancy Check (CRC) generation and checking. The LCC is
controlled by the Z-80B through local (card resident) memory.
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