User guide

VIF_ABR (VME_IF_BASE + 184) defines the base address of the Alpha VME 4
system in each VMEbus address space as shown in Figures 10–7 and 10–8.
Figure 10–7 Address Decoding
31 08 00
ML013341
VME A32 Addr
152324 0716
VME A24 Addr
VME A16 Addr
= Region of address which can be compared to form base address
Associated with each of the top three comparison bytes is a bit mask to control
the number of bits that are checked during a VMEbus address match. These
bits are contained in VIF_MASK at VME_IF_BASE + 0x180. If a bit is set, the
address-to-base register bit is not used in the address comparison. At least the
top five bits of the A32 address match byte must be used for matching.
Bytes 1 through 3 of VIF_ABR and VIF_MASK are contained in CY7C964
elements. These three bytes must be written simultaneously. Byte 0 is not
used and does not affect address recognition. See the CY7C964 specification for
more detail on the comparison and mask registers.
Figure 10–8 Base and Mask Register
ML013374
Comparison for A32 Addr <31:24>
Comparison for A24 Addr <23:16>
Comparison for A16 Addr <15:8>
Byte 3
VIF_ABR
Byte 2Byte 1 Byte 0
ICR
VME_IF_BASE + 184:
VME Interface 10–11