Motorola MCP750 Specifications download pdf (Page 57)

Series 6000 Hardware Environmen

4-9

then the device vendor must build a programmable assembly for a suitable

address.

NOTE

Installing components not specified or marketed by the device

vendor might void the warranty. Patent and copyrights that apply

to the device also cover programmable assemblies, which require

written permission from the vendor to modify or copy. (License

fees might accompany such permission.) With such permission,

Concurrent Computer Corporation can provide PALs to address

third-party devices. A different -90x number for each valid

address on the top-level assembly number identifies PALs sup-

plied by Concurrent Computer Corporation.

Bus Arbitration 4

Busses that support multiple bus masters must provide a means of resolving the contention

of concurrent requests for bus mastership by multiple devices. This is the purpose of a spe-

cial unit on the (H)VME bus, the (H)VME bus arbiter.

Bus arbitration is important only for devices that can act as bus masters. Device speciﬁca-

tions indicate this ability as either “bus master” or “DMA Operation.” Because bus arbitra-

tion depends on implementation, the following sections explain arbitration on the Series

6000 platform.

Bus Request Levels 4

The VMEbus specification defines extensive bus arbitration options implemented in

HVME by the following signals:

• Bus request level BR0

• Bus grant BG0 (BG0IN, BG0OUT)

• Bus busy (BBSY) signal.

Each slot has a BR0xx signal (where xx refers to the slot number) driven to the bus arbiter.

The bus arbiter directly drives a BG0xx signal (where xx refers to the slot number) to the

appropriate slot. This eliminates the latency of daisy chaining the bus grants and can also

configure specific slots for round-robin arbitration. All slots receive the BBSY signal,

when appropriate.

Devices on the (H)VME bus become the bus master by asserting bus request and receiving

bus grant. The new bus master asserts the bus busy (BBSY) signal until relinquishing the

bus. During this time, only it can generate bus addresses.

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Motorola MCP750 Specifications Page 57