Freescale Semiconductor Demonstration Board for Freescale MC9S12XHY256 Microcontroller DEMO9S12XHY256 DEMO9S12XHY256 Manual De Usuario
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DEMO9S12XHY256
S12X Debug (S12XDBGV3) Module
MC9S12XHY-Family Reference Manual, Rev. 1.04
248
Freescale Semiconductor
NOTE
Using this configuration, a byte access of ADDR[n] can cause a comparator match if the databus low byte
by chance contains the same value as ADDR[n+1] because the databus comparator does not feature access
size comparison and uses the mask as a “don’t care” function. Thus masked bits do not prevent a match.
by chance contains the same value as ADDR[n+1] because the databus comparator does not feature access
size comparison and uses the mask as a “don’t care” function. Thus masked bits do not prevent a match.
Comparators A and C feature an NDB control bit to determine if a match occurs when the data bus differs
to comparator register contents or when the data bus is equivalent to the comparator register contents.
to comparator register contents or when the data bus is equivalent to the comparator register contents.
6.4.2.2
Exact Address Comparator Match (Comparators B and D)
Comparators B and D feature SZ and SZE control bits. If SZE is clear, then the comparator address match
qualification functions the same as for comparators A and C.
qualification functions the same as for comparators A and C.
If the SZE bit is set the access size (word or byte) is compared with the SZ bit value such that only the
specified type of access causes a match. Thus if configured for a byte access of a particular address, a word
access covering the same address does not lead to match.
specified type of access causes a match. Thus if configured for a byte access of a particular address, a word
access covering the same address does not lead to match.
6.4.2.3
Data Bus Comparison NDB Dependency
Comparators A and C each feature 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.
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 (DBGxDHM/DBGxDLM), 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.
clearing the corresponding mask bit (DBGxDHM/DBGxDLM), 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.
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 6-37. Comparator Access Size Considerations
Comparator
Address
SZE
SZ8
Condition For Valid Match
Comparators
A and C
ADDR[n]
—
—
Word and byte accesses of ADDR[n]
(1)
MOVB #$BYTE ADDR[n]
MOVW #$WORD ADDR[n]
1. A word access of ADDR[n-1] also accesses ADDR[n] but does not generate a match.
The comparator address register must contain the exact address used in the code.
Comparators
B and D
ADDR[n]
0
X
Word and byte accesses of ADDR[n]
1
MOVB #$BYTE ADDR[n]
MOVW #$WORD ADDR[n]
Comparators
B and D
ADDR[n]
1
0
Word accesses of ADDR[n]
1
MOVW #$WORD ADDR[n]
Comparators
B and D
ADDR[n]
1
1
Byte accesses of ADDR[n]
MOVB #$BYTE ADDR[n]