Motorola MCP750 Specifications download pdf (Page 83)

PowerMAXION Hardware Environmen

6-5

Transfer Width Support 6

For all non-block mode transfers, byte, word and long-word addresses are supported. Byte

addresses are supported on even and odd addresses. Word addresses (16-bit) are supported

on even addresses. Longword transfers are supported on longword addresses. Only long-

word transfers are supported using VME Block Mode Transfers (BMT).

Address Types 6

Bus masters on the VME I/O bus can use different types of addresses dynamically:

short(16 bit-address), standard (24-bit addresses), or extended (32-bit addresses).

The source of the addresses can either be local to the VME bus or come from the proces-

sor acting as bus master.

Short address accesses are local to the VME I/O bus on which they originate. Standard

addresses access either system memory (below 12MB) or memory local to the VME bus.

Extended addresses access all of system memory.

Address Modiﬁers 6

For each data transfer on the VME bus, the bus master (either a processor or an I/O device)

must identify the characteristics of the data transfer by sending a special six-bit code along

with the transfer. This code is called an address modifier. For each different type of data

transfer there is one unique address modiﬁer value to be used. The address modiﬁer speci-

ﬁes the address type (short, standard, extended), the access method (a single location or a

series of locations), and the data access privilege (supervisory or non-privileged).

If the transfer originates with the processor, the VME I/O interface generates the appropri-

ate address modiﬁer. If the device initiates the transfer, the device controller generates the

address modiﬁer. Sometimes the address modiﬁer is hard-wired into the device controller;

other times it can be selected via jumpers or switches on the device. Alternatively, some

devices use programmable address modifiers. Refer to the device Installation manual for

the proper setting of the address modiﬁer when it is conﬁgurable.

For additional information on address modifiers, refer to the PowerMAXION Architecture

Manual.

VME Address Ranges 6

The following sections explain the address ranges used by VME devices on the VME I/O

bus when they are bus masters or bus slaves.

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Motorola MCP750 Specifications Page 83