Data General AViiON 4600 Series, Customer Documentation

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Using the SCM Configuration Menus
5-19
014–002091
Changing the VME A24 Configuration
It is very unlikely that you will ever needto complete the steps in this section. The
Change VME A24 Configuration menu allows you to alter the way default system
address mapping allows access to VME A24 space.
You do not need to reconfigure A24
space if you purchased VME controllers from Data General.
CAUTION : Do not make changes in the VME A24 configuration menu unless you
have one or more A24-type controllers
you are familiar with VME
programming and configuration concepts.
Logic within the system board controls access to portions of system address space.
Address decoders, in conjunction with programmable address maps, regulate accesses
to and from the system board. The Mbus Address Decoder (MAD) enables Mbus
access, and the VMEbus Address Decoder (VAD) enables access from a VME controller
to a location or resource in system memory. MAD andVAD mapping determine, in
part, how the system accesses the 16 megabytes of A24 address space. At powerup,
PROM code loads and verifies the MAD and VAD to default values. The Change VME
A24 configuration" menu allows you to change this default A24 space mapping.
An A24 board that directs data transfers between itself and other VMEbus boards
contains a
MASTER module . If the same boardcontains memory accessible from the
VMEbus, it also contains a SLAVE module . When a VME A24 Location Module is in
SLAVE mode, it detects Data Transfer Bus (DTB) cycles initiated by a MASTER and
can transfer data between itself and the MASTER. When A24 is in MASTER mode, it
initiates DTB cycles in order to transfer data between itself and a SLAVE module.
Since A24 space is partitionedinto four 4-megabyte pages, you can specify which
pages of A24 Address space function in SLAVE mode and which are in MASTER mode
using this menu.
The combination, type, anduse of VME A24 controllers in your system determine how
you should configure A24 address space.
Refer to your Programming System Control and I/O Registers manual for more
information about memory maps and address decoding.
To change the default VME A24 configuration, type andpress New Line while in the
View or Change System Configuration menu to select item 6, Change VME A24
configuration." The system displays the following menu: