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The 8XC196NT has two power saving modes: idle and powerdown. It also provides 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 Appendix B for descriptions of
signal status during each mode, and to Appendix C for details about the registers.)
13.1 SPECIAL OPERATING MODE SIGNALS AND REGISTERS
Table 13-1 lists the signals and Table 13-2 lists the registers that are mentioned in this chapter.
Signal
Port Pin
Name
P2.7
CLKOUT
P2.2
EXTINT
P2.6
ONCE#
SPECIAL OPERATING MODES
Table 13-1. Operating Mode Control Signals
Type
O
Clock Output
Output of the internal clock generator. The CLKOUT frequency is ½
the oscillator input frequency (XTAL1). CLKOUT has a 50% duty cycle.
I
External Interrupt
In normal operating mode, a rising edge on EXTINT sets the EXTINT
interrupt pending bit. EXTINT is sampled during phase 2 (CLKOUT
high). The minimum high time is one state time.
If the chip is in idle mode and if EXTINT is enabled, a rising edge on
EXTINT brings the chip back to normal operation, where the first
action is to execute the EXTINT service routine. After completion of
the service routine, execution resumes at the the IDLPD instruction
following the one that put the device into idle mode.
In powerdown mode, asserting EXTINT causes the chip to return to
normal operating mode. If EXTINT is enabled, the EXTINT service
routine is executed. Otherwise, execution continues at the instruction
following the IDLPD instruction that put the device into powerdown
mode.
I
On-circuit Emulation
Holding ONCE# low during the rising edge of RESET# places the
device into on-circuit emulation (ONCE) mode. This mode puts all pins
into a high-impedance state, thereby isolating the device from other
components in the system. The value of ONCE# is latched when the
RESET# pin goes inactive. While the device is in ONCE mode, you
can debug the system using a clip-on emulator. To exit ONCE mode,
reset the device by pulling the RESET# signal low. To prevent
inadvertent entry into ONCE mode, either configure this pin as an
output or hold it high during reset and ensure that your system meets
the V
specification (see datasheet).
IH
CHAPTER 13
Description
13-1
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