CPU16
REFERENCE MANUAL
DEVELOPMENT SUPPORT
MOTOROLA
10-11
10.4.2 BDM Sources
When BDM is enabled, external breakpoint hardware, internal IMB module break-
points, and the BGND instruction can cause the CPU16 to enter BDM. If BDM is not
enabled when a breakpoint occurs, a breakpoint exception is processed.
Table 10-2
summarizes the processing of each source for both enabled and disabled cases.
10.4.2.1 BKPT Signal
If enabled, BDM is initiated when assertion of BKPT is acknowledged. BKPT can be
asserted on the IMB by another module in the microcontroller, or by taking the micro-
controller BKPT pin low. There is no breakpoint acknowledge bus cycle when BDM is
entered. See the appropriate microcontroller user's manual for more information con-
cerning assertion of BKPT.
10.4.2.2 BGND Instruction
If BDM has been enabled, executing BGND will cause the CPU16 to suspend normal
operation and enter BDM. If BDM has not been correctly enabled, an illegal instruction
exception is generated. Illegal instruction exceptions are discussed in
SECTION 9 EX-
CEPTION PROCESSING
.
10.4.2.3 Microcontroller Module Breakpoints
If BDM has been enabled, the CPU16 will enter BDM when other microcontroller mod-
ules assert the BKPT signal. Consult the appropriate microcontroller user's manual for
a description of these capabilities.
10.4.2.4 Double Bus Fault
If BDM has been enabled, the CPU16 will enter BDM when a double bus fault is de-
tected. If BDM has not been enabled, the HALT signal is asserted and processing
stops.
10.4.3 BDM Signals
When BDM is entered, the BKPT and IPIPE signals change function and become BDM
serial communication signals. The following table summarizes the changes.
Table 10-2 BDM Source Summary
Source
BKPT
BDM Enabled
Background
Background
Background
BDM Disabled
Breakpoint Exception
Illegal Instruction
Assert HALT
BGND Instruction
Double Bus Fault
F
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