TC1796
System Units (Vol. 1 of 2)
LMB External Bus Unit
User’s Manual 13-30 V2.0, 2007-07
EBU, V2.0
13.5.3 Address Comparison
Standard Address Comparison Mode
When an Addressing Override Mode is not active, each of the five EBU regions can be
programmed for independent base addresses and lengths by bits and bit fields in
registers EBU_ADDRSELx and EBU_EMU_AS.
• Bit REGEN is the enable control of a region. If the region is disabled (REGEN = 0),
no address comparison will take place for the region.
• Bit field BASE specifies address bits A[31:12] of region x, where A[31:28] must only
point to segments 8, 10, 13, and 14 (see Table 13-9 on Page 13-25).
• Bit field MASK determines the length of a region. It specifies how many bits of a
PLMB address must match the contents of the BASE(x) bit field (to a maximum of 15,
starting with A[26]). Note that address bits A[31:27] must always match.
• Bit field ALTSEG determines the number of an alternate segment that can be used
for address comparison with A[31:28] (if enabled by ALTENAB = 1).
• Bit ALTENAB determines whether an additional alternate segment number as
defined by ALTSEG is used for address comparison.
The Emulator Address Select register EBU_EMUAS has identical functionality as the
EBU_ADDRSELx register.
The address comparison scheme is shown in Figure 13-11.
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