MC68HC912B32 Datasheet, PDF (123/128 Pages) Motorola, Inc – 16-Bit Microcontroller

16.3 Breakpoints
Hardware breakpoints are used to debug software on the MC68HC912B32 by comparing actual ad-
dress and data values to predetermined data in setup registers. A successful comparison will place the
CPU in background debug mode (BDM) or initiate a software interrupt (SWI). Breakpoint features de-
signed into the MC68HC912B32 include:
• Mode selection for BDM or SWI generation
• Program fetch tagging for cycle of execution breakpoint
• Second address compare in dual address modes
• Range compare by disable of low byte address
• Data compare in full feature mode for non-tagged breakpoint
• Byte masking for high/low byte data compares
• R/W compare for non-tagged compares
• Tag inhibit on BDM TRACE
16.3.1 Breakpoint Modes
Three modes of operation determine the type of breakpoint in effect.
• Dual address-only breakpoints, each of which will cause a software interrupt (SWI)
• Single full-feature breakpoint which will cause the part to enter background debug mode (BDM)
• Dual address-only breakpoints, each of which will cause the part to enter BDM
Breakpoints will not occur when BDM is active.
16.3.1.1 SWI Dual Address Mode
In this mode, dual address-only breakpoints can be set, each of which cause a software interrupt. This
is the only breakpoint mode which can force the CPU to execute a SWI. Program fetch tagging is the
default in this mode; data breakpoints are not possible. In the dual mode each address breakpoint is
affected by the BKPM bit and the BKALE bit. The BKxRW and BKxRWE bits are ignored. In dual ad-
dress mode the BKDBE becomes an enable for the second address breakpoint. The BKSZ8 bit will
have no effect when in a dual address mode.
16.3.1.2 BDM Full Breakpoint Mode
A single full feature breakpoint which causes the part to enter background debug mode. BDM mode
may be entered by a breakpoint only if an internal signal from the BDM indicates background debug
mode is enabled.
• Breakpoints are not allowed if the BDM mode is already active. Active mode means the CPU is
executing out of the BDM ROM.
• BDM should not be entered from a breakpoint unless the ENABLE bit is set in the BDM. This is
important because even if the ENABLE bit in the BDM is negated the CPU actually does execute
the BDM ROM code. It checks the ENABLE and returns if not set. If the BDM is not serviced by
the monitor then the breakpoint would be re-asserted when the BDM returns to normal CPU flow.
• There is no hardware to enforce restriction of breakpoint operation if the BDM is not enabled.
16.3.1.3 BDM Dual Address Mode
Dual address-only breakpoints, each of which cause the part to enter background debug mode. In the
dual mode each address breakpoint is affected, consistent across modes, by the BKPM bit, the BKALE
bit, and the BKxRW and BKxRWE bits. In dual address mode the BKDBE becomes an enable for the
second address breakpoint. The BKSZ8 bit will have no effect when in a dual address mode. BDM mode
may be entered by a breakpoint only if an internal signal from the BDM indicates background debug
mode is enabled.
• BKDBE will be used as an enable for the second address only breakpoint.
MC68HC912B32
MC68HC912B32TS/D
MOTOROLA
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