Motorola MVME162P-242, Installation And Use Manual

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Functional Description
http://www.motorola.com/computer/literature 4-17
4
µ
sec, 64
µ
sec, 256
µ
sec, or infinity. The local bus timer does not operate
during VMEbus bound cycles. VMEbus bound cycles are timed by the
VMEbus access timer and the VMEbus global timer. Refer to the
VMEchip2 and Petra/MC2 descriptions in the MVME1X2P2 VME
Embedded Controller Programmer’s Reference Guide for detailed
programming information.
The access timer logic is duplicated in the VMEchip2 and Petra/MC2
ASICs. Because the local bus timer in the VMEchip2 can detect an
offboard access and the Petra/MC2 local bus timer cannot, the timer in the
VMEchip2 ASIC is used in all cases except for versions of the
MVME162P2 which do not include the VMEbus interface (i.e., boards
ordered with a "No VMEbus Interface" option).
Local Bus Arbiter
The local bus arbiter implements a fixed priority (see Table 4-2 ).
Table 4-2. Local Bus Arbitration Priority
Device Priority Note
LAN 0 Highest
Industry Pack DMA 1
SCSI 2 ...
VMEbus 3 Next Lowest
MC680x0/MC68LC0x0 4 Lowest