mc68hc908sr12 Freescale Semiconductor, Inc, mc68hc908sr12 Datasheet - Page 171

• Manufacturer Part Number: mc68hc908sr12
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

MC68HC908SR12•MC68HC08SR12 — Rev. 5.0
Freescale Semiconductor
Figure 10-2
the reset vector is blank and just 1 x V
pin. An external oscillator of 9.8304 MHz is required for a baud rate of
9600, as the internal bus frequency is automatically set to the external
frequency divided by four.
Enter monitor mode with pin configuration shown in
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
break signal (10 consecutive logic 0s) to the host, indicating that it is
ready to receive a command.
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.
Figure 10-2. Low-Voltage Monitor Mode Entry Flowchart
10.5
shows a simplified diagram of the monitor mode entry when
Monitor ROM (MON)
Security.) After the security bytes, the MCU sends a
MONITOR MODE
TRIGGERED?
POR RESET
IS VECTOR
EXECUTE
MONITOR
BLANK?
CODE
POR
YES
YES
NO
NO
DD
voltage is applied to the IRQ1
NORMAL USER
MODE
Figure 10-1
Functional Description
Monitor ROM (MON)
Data Sheet
by
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