User guide

In addition to these four bus release modes, the scatter-gather RMW bit (RMC)

can be used to force Digital Alpha VME 4 to hold ownership of the VMEbus for

two accesses before releasing in the programmed ROR, RWD, or ROC fashion.

See Section 10.1.2 for details.

Figure 10–12 VIC Release Control Register

31 07 06 05 00

ML013330

VMEbus Release Protocol

DMA Burst Length

Don't Care

VME_IF_BASE+D0 :

VIC_RCR

Table 10–8 VIC Release Control Register

Field Name Description

<5:0> DMA burst

length

Speciﬁes the number of data transfers during a burst on the

VMEbus. For example, a value of 4 means that 4 words are

transferred in D16, or, in D32, it means 4 longwords. For D64

block-mode operation, the burst-length value is multiplied by

four to give the maximum number of data transfers before

giving up the bus. This means a maximum burst length value

of 64 allows 256 (64x4) transfers of D64 data, which is 2048

bytes.

(continued on next page)

10–20 VME Interface