Chapter 3. STD Bus Interface
27
Multiple Master
A multiple master architecture requires one permanent master and one or more temporary masters,
as illustrated in the "Multiple Master Architecture" figure below. The ZT 8905 is configurable for either
permanent or temporary master operation. Each master has complete access to STD bus resources
and operates at full speed when the local CPU is communicating with local memory and I/O. It is not
until the application software attempts an STD bus access that arbitration occurs.
The ZT 8905 responds to an STD bus access from the application software by generating an
STD bus request, MREQx* (E70), to an external bus arbiter, such as the ZT 89CT39. The
ZT 89CT39 must be Revision D or higher. The ZT 8905 then suspends all local operation until the
bus arbiter returns an STD bus acknowledge, MAKx* (E69). All arbitration is done in hardware on the
external bus arbiter board and is transparent to the application software. The amount of time required
for this arbitration depends on the amount of time higher priority masters are in control of STD bus
resources. A shared resource locking mechanism is supported to guarantee exclusive access to
STD bus memory or I/O.
I/O SLAVE
MEMORY SLAVE
ZT 8905
TEMPORARY
MASTER
ZT 8905
TEMPORARY
MASTER
ZT 8905
TEMPORARY
MASTER
ZT 8905
PERMANENT
MASTER
SLOT X
ARBITER
TM
ZT200
Embedded
Computer
Multiple Master Architecture
Intelligent I/O
An intelligent I/O system includes a single ZT 8905 and one or more intelligent I/O boards, such as
the ZT 8832. This architecture is illustrated in the "Intelligent I/O Architecture" figure on the following
page. The intelligent I/O board incorporates several I/O devices, a dual-port RAM for processor
communications, and a CPU dedicated to controlling these devices.
Each intelligent I/O board operates at full speed when communicating with local memory, local I/O,
and dual-port RAM. The ZT 8905 also operates at full STD bus speeds when accessing the dual-port
RAM. It is not until the ZT 8905 and the intelligent I/O board access the dual-port RAM at the same
time that arbitration occurs.
All arbitration is done in hardware local to each intelligent I/O board, eliminating the need for an
external bus arbiter. The arbitration is transparent to the application software. The amount of time
required for arbitration depends on the amount of time the device in control of the dual-port RAM
requires to complete operation. A shared resource locking mechanism is supported to guarantee
exclusive access to dual-port RAM by either the ZT 8905 or the intelligent I/O board.
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Содержание ZT 8905
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