SYS68K/CPU-30 R4 Technical Reference Manual
Hardware Description
Page 103
3.20 VMEbus Arbitration
Each transfer to/from an off-board address causes a VMEbus access
cycle. The VMEbus defines an arbitration mechanism to arbitrate for bus
mastership. The CPU board includes a VMEbus requester, so that it may
access external VMEbus resources, and a VMEbus arbiter, so that it may
optionally act as "Slot-1" system controller.
3.20.1 Single-Level
VMEbus
Arbiter
The CPU board contains a single level arbiter which can be
enabled/disabled through software. No additional control of the arbiter is
required.
NOTE: In accordance with the VMEbus specification, the arbiter must
be enabled if the CPU board is located in the first slot of the VMEbus
backplane, and that it must be disabled if the CPU board is located in any
other slot.
When the on-board single-level VMEbus arbiter is enabled, all other
VMEbus masters (if any) must request VMEbus master ship using only
bus request level 3 (BR3*), or they will not be recognized by the CPU
board.
3.20.2 VMEbus
Requester
The CPU board includes a VMEbus requester so that it may access
external VMEbus resources. The level of the request may be selected by
switches if the CPU-30 R4 did not detect slot-1.
In the case that the CPU-30 R4 detects slot-1, the request level 3 will be
used automatically.
SEE ALSO: For a detailed description of the slot-1 detection please refer
to Section 3.21, ‘Slot-1 Detection,’ on page 107.
NOTE: Note that the selection of the VMEbus request level has no effect
upon the VMEbus arbiter located in the FGA-002 Gate Array.
SW6-3
SW6-4
Default
Position
Description
OFF
OFF
x
Request level 3
OFF
ON
Request level 2
ON
OFF
Request level 1
ON
ON
Request level 0
i
☞
i
Содержание SYS68K/CPU-30 R4
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Страница 145: ...VMEPROM SYS68K CPU 30 R4 Technical Reference Manual Page 132...
Страница 189: ...Appendix to VMEPROM SYS68K CPU 30 R4 Technical Reference Manual Page 176...