
MOTOROLA
5-34
SINGLE-CHIP INTEGRATION MODULE 2
MC68HC16R1/916R1
USER’S MANUAL
During a CPU space access, ADDR[19:16] are encoded to reflect the type of access
being made. Three encodings are used by the MCU, as shown in
Figure 5-13
. These
encodings represent breakpoint acknowledge (Type $0) cycles, low power stop
broadcast (Type $3) cycles, and interrupt acknowledge (Type $F) cycles. Type $0 and
type $3 cycles are discussed in the following paragraphs. Refer to
5.8 Interrupts
for
information about interrupt acknowledge bus cycles.
Figure 5-13 CPU Space Address Encoding
5.6.4.1 Breakpoint Acknowledge Cycle
Breakpoints stop program execution at a predefined point during system development.
In the MC68HC16R1/916R1, breakpoints are treated as a type of exception process-
ing. Breakpoints can be used alone or in conjunction with background debug mode.
The MC68HC16R1/916R1 has only one source and type of breakpoint. This is a
hardware breakpoint initiated by assertion of the BKPT input. Other modular
microcontrollers may have more than one source or type. The breakpoint
acknowledge cycle discussed here is the bus cycle that occurs as a part of breakpoint
exception processing when a breakpoint is initiated while background debug mode is
not enabled.
BKPT is sampled on the same clock phase as data. BKPT is valid, the data is tagged
as it enters the CPU16 pipeline. When BKPT is asserted while data is valid during an
instruction prefetch, the acknowledge cycle occurs immediately after that instruction
has executed. When BKPT is asserted while data is valid during an operand fetch, the
acknowledge cycle occurs immediately after execution of the instruction during which
it is latched. BKPT is asserted for only one bus cycle and a pipe flush occurs before
BKPT is detected by the CPU16, no acknowledge cycle occurs. To ensure detection,
BKPT should be asserted until a breakpoint acknowledge cycle is recognized.
CPU SPACE CYC TIM
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
T 0
BKPT#
19
23
16
0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0
19
16
23
1 1 1
1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1
1 1 1
LEVEL
19
16
23
CPU SPACE CYCLES
FUNCTION
CODE
2
0
2
0
2
0
0
0
0
CPU SPACE
TYPE FIELD
ADDRESS BUS
BREAKPOINT
ACKNOWLEDGE
LOW POWER
STOP BROADCAST
INTERRUPT
ACKNOWLEDGE
2
4
1