S12S Debug Module (S12SDBGV2)
6.4.2.1.4
Comparator A Data Bus Comparison NDB Dependency
Comparator A features an NDB control bit, which allows data bus comparators to be configured to either
trigger on equivalence or trigger on difference. This allows monitoring of a difference in the contents of
an address location from an expected value.
When matching on an equivalence (NDB=0), each individual data bus bit position can be masked out by
clearing the corresponding mask bit (DBGADHM/DBGADLM) so that it is ignored in the comparison. A
match occurs when all data bus bits with corresponding mask bits set are equivalent. If all mask register
bits are clear, then a match is based on the address bus only, the data bus is ignored.
When matching on a difference, mask bits can be cleared to ignore bit positions. A match occurs when any
data bus bit with corresponding mask bit set is different. Clearing all mask bits, causes all bits to be ignored
and prevents a match because no difference can be detected. In this case address bus equivalence does not
cause a match.
Table 6-35. NDB and MASK bit dependency
DBGADHM[n] /
NDB
Comment
DBGADLM[n]
0
0
1
1
0
1
0
1
Do not compare data bus bit.
Compare data bus bit. Match on equivalence.
Do not compare data bus bit.
Compare data bus bit. Match on difference.
6.4.2.2
Range Comparisons
Using the AB comparator pair for a range comparison, the data bus can also be used for qualification by
using the comparator A data registers. Furthermore the DBGACTL RW and RWE bits can be used to
qualify the range comparison on either a read or a write access. The corresponding DBGBCTL bits are
ignored. The SZE and SZ control bits are ignored in range mode. The comparator A TAG bit is used to tag
range comparisons. The comparator B TAG bit is ignored in range modes. In order for a range comparison
using comparators A and B, both COMPEA and COMPEB must be set; to disable range comparisons both
must be cleared. The comparator A BRK bit is used to for the AB range, the comparator B BRK bit is
ignored in range mode.
When configured for range comparisons and tagging, the ranges are accurate only to word boundaries.
6.4.2.2.1
Inside Range (CompA_Addr ≤ address ≤ CompB_Addr)
In the Inside Range comparator mode, comparator pair A and B can be configured for range comparisons.
This configuration depends upon the control register (DBGC2). The match condition requires that a valid
match for both comparators happens on the same bus cycle. A match condition on only one comparator is
not valid. An aligned word access which straddles the range boundary is valid only if the aligned address
is inside the range.
S12P-Family Reference Manual, Rev. 1.13
178
Freescale Semiconductor
FREESCALE [ Freescale ]
