Address Decoding; Base And Mask Register - DEC Digital Alpha VME 4/224 User Manual

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
VME A32 Addr
VME A24 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
VME_IF_BASE + 184:
VIF_ABR
Comparison for A32 Addr <31:24>
Comparison for A24 Addr <23:16>
Comparison for A16 Addr <15:8>
24 23 16 15
VME A16 Addr
Byte 3 Byte 1
08 07 00
ML013341
Byte 2 Byte 0
ICR
ML013374
VME Interface 10–11