MC68HC908QC16_07 Datasheet, PDF (224/274 Pages) Freescale Semiconductor, Inc – Microcontrollers

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BCFE — Break Clear Flag Enable Bit
This read/write bit enables software to clear status bits by accessing status registers while the MCU is
in a break state. To clear status bits during the break state, the BCFE bit must be set.
1 = Status bits clearable during break
0 = Status bits not clearable during break
18.2.3 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes. If enabled, the
break module will remain enabled in wait and stop modes. However, since the internal address bus does
not increment in these modes, a break interrupt will never be triggered.
18.3 Monitor Module (MON)
The monitor module allows debugging and programming of the microcontroller unit (MCU) through a
single-wire interface with a host computer. Monitor mode entry can be achieved without use of the higher
test voltage, V_TST, as long as vector addresses $FFFE and $FFFF are blank, thus reducing the hardware
requirements for in-circuit programming.
Features include:
• Normal user-mode pin functionality
• One pin dedicated to serial communication between MCU and host computer
• Standard non-return-to-zero (NRZ) communication with host computer
• Standard communication baud rate (7200 @ 2-MHz bus frequency)
• Execution of code in random-access memory (RAM) or FLASH
• FLASH memory security feature⁽¹⁾
• FLASH memory programming interface
• Use of external 9.8304 MHz oscillator to generate internal frequency of 2.4576 MHz
• Simple internal oscillator mode of operation (no external clock or high voltage)
• Monitor mode entry without high voltage, V_TST, if reset vector is blank ($FFFE and $FFFF contain
$FF)
• Normal monitor mode entry if V_TST is applied to IRQ
18.3.1 Functional Description
Figure 18-9 shows a simplified diagram of monitor mode entry.
The monitor module receives and executes commands from a host computer. Figure 18-10, Figure 18-11,
and Figure 18-12 show example circuits used to enter monitor mode and communicate with a host
computer via a standard RS-232 interface.
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or copying the FLASH difficult for
unauthorized users.
MC68HC908QC16 • MC68HC908QC8 • MC68HC908QC4 Data Sheet, Rev. 3
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Freescale Semiconductor