Intel 386 manual Local BUS Extension iLBX, Serial System BUS iSSB

MULTIBUS II AND Intel386 DX MICROPROCESSOR

decoder distinguishes between local, interconnect, and iPSB accesses. PLDs control the buffering of signals between the Intel386 DX microprocessor, BAC, MIC, 8751 Micro- controller, and iPSB bus.

10.3 LOCAL BUS EXTENSION (iLBX II)

The iLBX II bus extension is a high-speed execution bus designed for quick access to off-board memory. One iLBX II bus extension can support either two processing sub- systems (called the primary requesting agent and the secondary requesting agent) plus four memory subsystems, or a single processing subsystem plus five memory subsystems. A MULTIBUS II system may contain more than one iLBX II bus extension to meet its memory requirements.

The iLBX II bus extension features a 26-bit address bus and a separate 32-bit data bus. Because these paths are separate, the extension allows pipelining of transfer cycles; the request phase of a transfer cycle can overlap the reply phase of the previous cycle.

Other features of the iLBX II bus extension are:

•A unidirectional handshake for fast data transfers

•Mutual exclusion capability to control multiported memory

•Interconnect space (for each bus agent) through which the primary requesting agent

initializes and configures all other bus agents. .

10.4 SERIAL SYSTEM BUS (iSSB)

The Serial System Bus (iSSB) provides a simple, low-cost alternative to the Parallel System Bus (iPSB) bus. In applications that do not require the high performance of the iPSB bus, the iSSB bus can provide some cost reduction. In systems containing both the iPSB bus and the iSSB bus, the iSSB bus provides an alternate path for interface control, diagnostics, or redundancy.

The iSSB bus can contain up to 32 bus agents distributed over a maximum of 10 meters. Bus control is determined through an access protocol called Carrier Sense Multiple Access with Collision Detection (CSMNCD). This protocol allows agents to transmit data whenever they are ready. In case of simultaneous transmission by two or more bus agents, the iSSB invokes a deterministic collision resolution algorithm to grant fair access to all agents.

From the application point of view, the error detection capability of the iSSB bus, cou- pled with an intelligent bus agent interface (able to retransmit) makes the iSSB bus as reliable as the iPSB bus, even though the iSSB bus may be up to 10 meters long.

10-7