3. STD Bus Interface
ÛZIATECH
33
Multiple Master Architecture
ZT8907
Intelligent I/O
An intelligent I/O system includes a single ZT 8907 and one or more intelligent I/O
boards, such as the ZT 8832. The "
" figure below illustrates
this 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 8907 also operates at full STD bus
speeds when accessing the dual-port RAM. It is not until the ZT 8907 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 8907 or the intelligent I/O board.
