M68ICS08GR datasheet(195/408 Pages) FREESCALE

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Monitor ROM (MON)

Functional Description

MC68HC908GR8 — Rev 4.0

Technical Data

MOTOROLA

Monitor ROM (MON)

195

Figure 15-2. Low-Voltage Monitor Mode Entry Flowchart

Enter monitor mode with pin configuration shown in Figure 15-1 by

pulling RST low and then high. The rising edge of RST latches monitor

mode. Once monitor mode is latched, the values on the specified pins

can change.

Once out of reset, the MCU waits for the host to send eight security

bytes. (See Security.) After the security bytes, the MCU sends a break

signal (10 consecutive logic 0s) to the host, indicating that it is ready to

receive a command.

NOTE:

The PTA1 pin must remain at logic 0 for 24 bus cycles after the RST pin

goes high to enter monitor mode properly.

In monitor mode, the MCU uses different vectors for reset, SWI

(software interrupt), and break interrupt than those for user mode. The

alternate vectors are in the $FE page instead of the $FF page and allow

code execution from the internal monitor firmware instead of user code.

NOTE:

Exiting monitor mode after it has been initiated by having a blank reset

vector requires a power-on reset. Pulling RST low will not exit monitor

mode in this situation.

IS VECTOR

BLANK?

POR

TRIGGERED?

NORMAL USER

MODE

MONITOR MODE

EXECUTE

MONITOR

CODE

YES

POR RESET

Freescale Semiconductor, Inc.

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