
EPC-9 Hardware Reference
5-2
5
5
VMEbus Arbitration
The bus arbiter supports the following arbitration modes:
•
Fixed Priority Arbitration (PRI)
•
Single Level arbitration (SGL), which is a subset of PRI
•
and Round Robin arbitration (RRS), which is the default setting.
The arbitration mode is selected in the Universe MISC_CTL register. The arbiter can
be programmed to timeout if the requester does not assert BBSY* within a specified
period. The timeout can be set to 16 us, 256 us, or disabled also via the MISC_CTL
register. 16 us is the default.
VMEbus Timeout
A programmable bus timer allows the VMEbus timeout period to be selected via the
MISC_CTL register. It can be programmed to 16 us, 32 us, 64 us, 128 us, 256 us,
512 us, 1024 us, or disabled. The default setting is 64 us. If a bus transaction times
out, the timer asserts the VMEbus BERR* signal.
VMEbus Requester
The Universe is software-configurable to request bus ownership on all VMEbus
request levels: BR3*, BR2*, BR1*, and BR0*. The default request level is BR3*.
Demand Mode is the default request mode.
The VMEbus requester can be configured in either Release-When-Done (RWD) or
Release-On-Request (ROR) mode. The default bus release mode is RWD.
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com