2

VMEchip2

always requests at the old level until it becomes bus master and the new level takes effect. If the VMEchip2 is bus master when the level is changed, the new level does not take effect until the bus has been released and re- requested at the old level. The requester always requests the VMEbus at level 3 the first time following a

SYSRESET.

 

0

VMEbus request level 0

 

1

VMEbus request level 1

 

2

VMEbus request level 2

 

3

VMEbus request level 3

DRELM

These bits define the VMEbus release mode for the

 

DMAC requester. The DMAC always releases the bus

 

when the FIFO is full (VMEbus to local bus) or empty

 

(local bus to VMEbus).

 

0

Release when the time on timer has expired

 

1

and a BRxsignal is active on the VMEbus.

 

Release when the time on timer has expired.

 

2

Release when a BRxsignal is active on the

 

 

VMEbus.

 

3

Release when a BRxsignal is active on the

 

 

VMEbus or the time on timer has expired.

DFAIR

When this bit is high, the DMAC requester operates in fair

 

mode. It waits until its request level is inactive before

 

requesting the VMEbus. When this bit is low, the DMAC

 

requester does not operate in fair mode.

DTBL

The DMAC operates in direct mode when this bit is low,

 

and it operates in command chaining mode when this bit

 

is high.

 

DEN

The DMAC is enabled when this bit is set high. This bit

 

always reads 0.

DHALT

When this bit is high, the DMAC halts at the end of a

 

command when the DMAC is operating in command

 

chaining mode. When this bit is low, the DMAC executes

 

the next command in the list.

2-56

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Page 146
Image 146
Motorola MVME1X7P manual Drelm, Dfair, Dtbl, Den, Dhalt