mc9s12vr48 Freescale Semiconductor, Inc, mc9s12vr48 Datasheet - Page 224

• Manufacturer Part Number: mc9s12vr48
• Description: S12 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

S12S Debug Module (S12SDBGV2)
6.4.2.1.4
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.
6.4.2.2
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
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
224
SZE
1
1
SZ
1
1
NDB
DBGADHM,
DBGADLM
Range Comparisons
0
0
1
1
Comparator A Data Bus Comparison NDB Dependency
Inside Range (CompA_Addr ≤ address ≤ CompB_Addr)
$FF00
$0000
DBGADHM[n] /
DBGADLM[n]
Byte
Byte, data(ADDR[n])=DH
0
1
0
1
Table 6-35. NDB and MASK bit dependency
MC9S12VR Family Reference Manual,
Preliminary - Subject to Change Without Notice
DH=DBGADH, DL=DBGADL
Access
Compare data bus bit. Match on equivalence.
Compare data bus bit. Match on difference.
Do not compare data bus bit.
Do not compare data bus bit.
Comment
Rev. 2.2
No databus comparison
Match data at ADDR[n]
Comment
Freescale Semiconductor