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14-1
CHAPTER 14
SPECIAL OPERATING MODES
The 8XC196MC, MD, and MH provide two power saving modes: idle and powerdown. They
also provide an on-circuit emulation (ONCE) mode that electrically isolates the device from the
other system components. This chapter describes each mode and explains how to enter and exit
each. (Refer to Appendix A for descriptions of the instructions discussed in this chapter, to Ap-
pendix B for descriptions of signal status during each mode, and to Appendix C for details about
the registers.)
14.1 SPECIAL OPERATING MODE SIGNALS AND REGISTERS
Table 14-1 lists the signals and Table 14-2 lists the registers that are mentioned in this chapter.
Table 14-1. Operating Mode Control Signals
Port Pin
Signal
Name
Type Description
P2.7 CLKOUT
(MC/MD
only)
O Clock Output
Output of the internal clock generator. The CLKOUT frequency is ½
the oscillator input frequency (F
XTAL1
). CLKOUT has a 50% duty cycle.
CLKOUT is not implemented on the 8XC196MH.
— EXTINT I External Interrupt
This programmable interrupt is controlled by the WG_PROTECT
register. This register controls whether the interrupt is edge triggered
or sampled and whether a rising edge/high level or falling edge/low
level activates the interrupt.
In powerdown mode, asserting the EXTINT signal for at least 50 ns
causes the device to resume normal operation. The interrupt need not
be enabled. If the EXTINT interrupt is enabled, the CPU executes the
interrupt service routine. Otherwise, the CPU executes the instruction
that immediately follows the command that invoked the power-saving
mode.
In idle mode, asserting any enabled interrupt causes the device to
resume normal operation.