3. STD Bus Interface
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masters do not drive SYSRESET*. The SYSRESET* activation can be disabled by
removing cuttable trace CT53. The ZT 8907 reset is typically active for 500 ms.
MULTIPLE MASTER AND INTELLIGENT I/O
Ziatech offers two architectures for increasing the number of microprocessors in a
single system: multiple master and intelligent I/O. Applications can use multiple master,
intelligent I/O, or a combination of the two. The following topics discuss the two
architectures.
Multiple Master
A multiple master architecture requires one permanent master and one or more
temporary masters, as illustrated in the "
" figure below. The
ZT 8907 is configurable (by installing or removing resistor packs RP1 and RP2) 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 8907 responds to an STD bus access from the application software by
generating an STD bus request, DREQx* (E16), to an external bus arbiter, such as the
ZT 89CT39. The ZT 8907 then suspends all local operation until the bus arbiter returns
an STD bus acknowledge, DAKx* (E15). The ZT 89CT39, if used, must be Revision D
or higher.
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.