Motorola MVME1X7P manual VMEchip2

Models: MVME1X7P

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VMEchip2

The requester requests the bus if any of the following conditions occur:

1.The local bus master initiates either a data transfer cycle or an interrupt acknowledge cycle to the VMEbus.

2.The chip is requested to acquire control of the VMEbus as signaled by the DWB input signal pin.

3.The chip is requested to acquire control of the VMEbus as signaled by the DWB control bit in the LCSR.

The local-bus-to-VMEbus requester in the VMEchip2 implements a fair mode. By setting the LVFAIR bit, the requester refrains from requesting the VMEbus until it detects its assigned request line in its negated state.

The local-bus-to-VMEbus requester attempts to release the VMEbus when the requested data transfer operation is complete, the DWB pin is negated, the DWB bit in the LCSR is negated and the bus is not being held by a lock cycle. The requester releases the bus as follows:

1.When the chip is configured in release-when-done (RWD) mode, the requester releases the bus when the above conditions are satisfied.

2.When the chip is configured in release-on-request (ROR) mode, the requester releases the bus when the above conditions are satisfied and there is a bus request pending on one of the VMEbus request lines.

To minimize the timing overhead of the arbitration process, the local-bus- to-VMEbus requester in the VMEchip2 executes an early release of the VMEbus. If it is about to release the bus and it is executing a VMEbus cycle, the requester releases BBSY before its associated master completes the cycle. This allows the arbiter to arbitrate any pending requests, and grant the bus to the next requester, at the same time that the active master completes its cycle.

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Motorola MVME1X7P manual VMEchip2