3. STD Bus Interface
28
I/O SLA
VE
MEMOR
Y SLA
VE
ZT 8904
TEMPORAR
Y
MASTER
ZT 8904
TEMPORAR
Y
MASTER
ZT 8904
TEMPORAR
Y
MASTER
ZT 8904
PERMANENT
MASTER
SLO
T X
ARBITER
TM
ZT200
Embedded
Computer
Multiple Master Architecture
Intelligent I/O
An intelligent I/O system includes a single ZT 8904 and one or more intelligent I/O
boards, such as the ZT 8832. This architecture is illustrated in the following figure
"
Intelligent I/O Architecture
." 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 8904 also operates at full STD bus
speeds when accessing the dual-port RAM. It is not until the ZT 8904 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 8904 or the intelligent I/O board.