Specifications

Power Hawk 610 Hardware Environmen
t
5-5
Figure 5-2. Big Endian Bit and Byte Notation
VME Addressing 5
This section describes the characteristics of data transfers on the VME bus. Doing so aids
in building device addresses and understanding the error detection and recovery feature of
the VMEbus.
Transfer Width Support 5
For all non-block mode transfers, VME supports byte, word and long-word addresses. It
supports byte addresses on even and odd addresses. It supports word addresses (16-bit) on
even addresses. It supports longword transfers on longword addresses.
VME Block Mode Transfers (BMT) only support longword addresses.
Address Types 5
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 reside on the local VME bus or come from the
processor acting as bus master.
Short address accesses come from sources local to the VME I/O bus on which they
originate. Standard addresses can access either system memory (below 12MB) or memory
local to the VME bus. Extended addresses access all of system memory.
LOW
ADDRESS
HIGHER
ADDRESS
LOW ADDRESS = MSB
MSB
LSB
7
0
15
16
23
24
31
0
0
7
8
7
8
15
MSB
LSB