Specifications

Power Hawk 620/640 Hardware Environmen
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VME Addressing 7
The main objective of this section is to help comprehend the characteristics of data
transfers on the VME bus. Understanding these characteristics aids in building device
addresses and understanding the error detection and recovery feature of the VMEbus.
Transfer Width Support 7
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 7
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
processor 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 7
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
specifies 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
appropriate 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 VMEbus standard
specification.