Intel Microcontroller, 80C196NU Exiting Standby Mode, Enabling and Disabling Powerdown Mode

SPECIAL OPERATING MODES

12.4.3 Exiting Standby Mode

The device will exit standby mode when a transition on an external interrupt pin (EXTINT3:0) or a hardware reset occurs. The interrupts need not be enabled for them to bring the device out of standby, but the pin must be configured as a special-function input (see “Bidirectional Port Pin Configurations” on page 7-7).

When an external interrupt brings the device out of standby mode, the corresponding pending bit is set in the interrupt pending register. If the interrupt is enabled, the device executes the interrupt service routine, then fetches and executes the instruction following the IDLPD #3 instruction. If the interrupt is disabled (masked), the device fetches and executes the instruction following the IDLPD #3 instruction and the pending bit remains set until the interrupt is serviced or software clears it.

12.5 POWERDOWN MODE

Powerdown mode places the device into a very low power state by disabling the internal oscilla- tor, the phase-locked loop circuitry (80C196NU only), and clock generators. Internal logic holds the CPU and peripheral clocks at logic zero, which causes the CPU to stop executing instructions, the system bus-control signals to become inactive, the CLKOUT signal to become high, and the peripherals to turn off. Power consumption drops into the microwatt range (refer to the datasheet for exact specifications). ICC is reduced to device leakage. Table B-5 on page B-13 lists the values of the pins during powerdown mode. If VCC is maintained above the minimum specification, the special-function registers (SFRs) and register RAM retain their data.

12.5.1 Enabling and Disabling Powerdown Mode

Setting the PD bit in the chip-configuration register 0 (CCR0.0) enables both standby and pow- erdown modes. Clearing it disables both modes. CCR0 is loaded from the chip configuration byte (CCB0) when the device is reset.

12.5.2 Entering Powerdown Mode

Before entering powerdown, complete the following tasks:

•Complete all serial port transmissions or receptions. Otherwise, when the device exits powerdown, the serial port activity will continue where it left off and incorrect data may be transmitted or received.

•Put all other peripherals into an inactive state.

•To allow other devices to control the bus while the microcontroller is in powerdown, assert HLDA#. Do this only if the routines for entering and exiting powerdown do not require access to external memory.

12-7