Datasheet

Chapter 16 Debug Module (DBGV1)
MC9S12E128 Data Sheet, Rev. 1.07
488 Freescale Semiconductor
16.3.2.8 Debug Control Register 3 (DBGC3)
Figure 16-14. Debug Control Register 3 (DBGC3)
1
RWCEN
Read/Write Comparator C Enable Bit — The RWCEN bit controls whether read or write comparison is enabled
for comparator C. RWCEN is not useful for tagged breakpoints.
0 Read/Write is not used in comparison
1 Read/Write is used in comparison
0
RWC
Read/Write Comparator C Value Bit — The RWC bit controls whether read or write is used in compare for
comparator C. The RWC bit is not used if RWCEN = 0.
0 Write cycle will be matched
1 Read cycle will be matched
76543210
R
BKAMBH
1
1
In DBG mode, BKAMBH:BKAMBL has no meaning and are forced to 0’s.
BKAMBL
1
BKBMBH
2
2
In DBG mode, BKBMBH:BKBMBL are used in full mode to qualify data.
BKBMBL
2
RWAEN RWA RWBEN RWB
W
Reset 0 0 0 00000
Table 16-15. DBGC3 Field Descriptions
Field Description
7:6
BKAMB[H:L]
Breakpoint Mask High Byte for First Address — In dual or full mode, these bits may be used to mask (disable)
the comparison of the high and/or low bytes of the first address breakpoint. The functionality is as given in
Table 16-16.
The x:0 case is for a full address compare. When a program page is selected, the full address compare will be
based on bits for a 20-bit compare. The registers used for the compare are {DBGCAX[5:0], DBGCAH[5:0],
DBGCAL[7:0]}, where DBGAX[5:0] corresponds to PPAGE[5:0] or extended address bits [19:14] and CPU
address [13:0]. When a program page is not selected, the full address compare will be based on bits for a 16-bit
compare. The registers used for the compare are {DBGCAH[7:0], DBGCAL[7:0]} which corresponds to CPU
address [15:0].
Note: This extended address compare scheme causes an aliasing problem in BKP mode in which several
physical addresses may match with a single logical address. This problem may be avoided by using DBG
mode to generate breakpoints.
The 1:0 case is not sensible because it would ignore the high order address and compare the low order and
expansion addresses. Logic forces this case to compare all address lines (effectively ignoring the BKAMBH
control bit).
The 1:1 case is useful for triggering a breakpoint on any access to a particular expansion page. This only makes
sense if a program page is being accessed so that the breakpoint trigger will occur only if DBGCAX compares.
Table 16-14. DBGC2 Field Descriptions (continued)
Field Description