![](http://datasheet.mmic.net.cn/120000/MC68349FT16_datasheet_3559370/MC68349FT16_85.png)
3- 34
MC68349 USER'S MANUAL
MOTOROLA
NOTE
The BKPT pin is sampled on the same clock phase as data
and is latched with data as it enters the CPU32+ pipeline. If
BKPT is asserted for only one bus cycle and a pipeline flush
occurs before BKPT is detected by the CPU32+, BKPT is
ignored. To ensure detection of BKPT by the CPU32+, BKPT
can be asserted until a breakpoint acknowledge cycle is
recognized.
When the MC68349 is configured for a 32-bit bus, the CPU32+
can fetch two instructions simultaneously. Since there is only
one BKPT pin, the external user cannot break individually on
those instructions, but rather must break on both, causing the
BKPT exception to be taken after the first instruction and
before the second instruction.
The breakpoint operation flowchart is shown in Figure 3-23. Figures 3-24 and 3-25 show
the timing diagrams for the breakpoint acknowledge cycle with instruction opcodes
supplied on the cycle and with an exception signaled, respectively.
3.4.2 LPSTOP Broadcast Cycle
The low power stop (LPSTOP) broadcast cycle is generated by the CPU32+ executing the
LPSTOP instruction. Since the external bus interface must get a copy of the interrupt
mask level from the CPU32+, the CPU32+ performs a CPU space type 3 write with the
mask level encoded on the data bus, as shown in the following figure. The CPU space
type 3 cycle waits for the bus to be available, and is shown externally to indicate to
external devices that the MC68349 is going into LPSTOP mode. If an external device
requires additional time to prepare for entry into LPSTOP mode, entry can be delayed by
asserting HALT. The SIM49 provides internal DSACK≈ response to this cycle. For more
information on how the SIM49 responds to LPSTOP mode, see Section 4 System
Integration Module.
31
19
18
17
16
—
I2I1I0
15
3
210
—
I2I1I0
I2–I0—Interrupt Mask Level
The interrupt mask level is encoded on bits 2–0 of the data bus during an LPSTOP
broadcast. For convenience when decoding, the interrupt mask level is replicated on
data bus bits 18–16 during an LPSTOP broadcast.