SPMCK16Z4MPV16 datasheet(147/500 Pages) FREESCALE

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M68HC16 Z SERIES

SYSTEM INTEGRATION MODULE

USER’S MANUAL

5-41

Figure 5-14 CPU Space Address Encoding

5.6.4.1 Breakpoint Acknowledge Cycle

Breakpoints stop program execution at a predefined point during system development.

In M68HC16 Z-series MCUs, breakpoints are treated as a type of exception process-

ing. Breakpoints can be used alone or in conjunction with background debug mode.

M68HC16 Z series MCUs have only one source and type of breakpoint. This is a hard-

ware breakpoint initiated by assertion of the BKPT input. Other modular microcontrol-

lers 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 process-

ing 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. If 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.

When BKPT assertion is acknowledged by the CPU16, the MCU performs a word read

from CPU space address $00001E. This corresponds to the breakpoint number field

(ADDR[4:2]) and the type bit (T) being set to all ones (source 7, type 1). If this bus cycle

is terminated by BERR or by DSACK, the MCU performs breakpoint exception pro-

cessing. Refer to Figure 5-15 for a flowchart of the breakpoint operation. Refer to the

SIM Reference Manual (SIMRM/AD) for further information.

CPU SPACE CYC TIM

0000000000000000000

BKPT#

000000111111111111111110

111

11111111111111111111

111

LEVEL

CPU SPACE CYCLES

FUNCTION

CODE

CPU SPACE

TYPE FIELD

ADDRESS BUS

BREAKPOINT

ACKNOWLEDGE

LOW POWER

STOP BROADCAST

INTERRUPT

ACKNOWLEDGE

Freescale Semiconductor, Inc.

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