Chapter 3. STD Bus Interface
28
I/O SLAVE
MEMORY SLAVE
ZT 8832
INTELLIGENT
I/O
ZT 8832
INTELLIGENT
I/O
ZT 8832
INTELLIGENT
I/O
ZT 8832
INTELLIGENT
I/O
ZT 8905
TM
ZT200
Embedded
Computer
Intelligent I/O Architecture
Multiple Master Vs. Intelligent I/O
Both multiple master and intelligent I/O architectures are excellent methods of increasing system
performance. The application designer has the freedom to select either architecture or combine both
to meet the needs of the specific application. The following is a brief comparison of the multiple
master and intelligent I/O architectures.
•
An advantage of the multiple master system is that each ZT 8905 has complete access to all
STD bus memory and I/O resources. In an intelligent I/O system, only the ZT 8905 has access to
STD bus memory and I/O, including the dual-port RAM interface to each intelligent I/O board.
•
An advantage of the intelligent I/O system is lower system cost. The intelligent I/O architecture
operates in both STD-80 and STD 32 bus structures. Dual port RAM arbitration is local to each
intelligent I/O board, eliminating the need for a system arbiter. Also, most multiple master
implementations require an STD bus memory slave for communications between the masters.
With an intelligent I/O architecture, all communications between the single master and the
intelligent I/O boards are through the dual-port RAM local to each intelligent I/O board.
Multiple Master System Requirements
The following is a list of considerations for the ZT 8905 operating in a multiple master architecture.
•
One ZT 8905 must be configured as a permanent master, or there must be another permanent
master in the system. The permanent master is responsible for managing the STD bus clock,
CLOCK* (P49), and the system reset, SYSRESET (P47). The remaining ZT 8905 boards must be
configured for temporary master operation.
To configure the ZT 8905 for permanent or temporary mode, RP2 and RP3 are used. Installing
these resistor packs configures the ZT 8905 for permanent master operation (the default);
removing them will configure the ZT 8905 for temporary master operation. These resistor packs
are located near the STD 32 gold fingers. RP2 and RP3 also provide pullup resistors for the SA
open collector signals on the STD 32 backplane. As there can only be one master that provides
the pullup mechanism, it is logical to always have the permanent master provide this feature. RP1
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Содержание ZT 8905
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