3. STD Bus Interface
29
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 8904
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 8904 has complete
access to all STD bus memory and I/O resources. However, in an intelligent I/O
system, only one ZT 8904 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 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.
System Requirements
The following is a list of considerations for the ZT 8904 operating in a multiple master
architecture.
•
One ZT 8904 must be configured as a permanent master, or there must be another
board in the system responsible for managing the STD bus clock, CLOCK* (P49),
and the system reset, SYSRESET (P47). The remaining ZT 8904 boards must be
configured for temporary master operation: the two socketed resistor packs, RP16
and RP17, must be installed on the permanent master and removed from all
temporary masters. These resistor packs are located next to the STD 32 connector.