NEC PD75P402, PD75402A user manual Standby Function, Stop mode, Halt mode

CHAPTER 7. STANDBY FUNCTION

CHAPTER 7. STANDBY FUNCTION

The μPD75402A has a standby function which can reduce the system power consumption. The standby function has the following two modes:

•STOP mode

•HALT mode

(1) STOP mode

In this mode, the main system clock oscillator is stopped and the whole system stops. The CPU current drain is reduced considerably.

Data memory low voltage (up to VDD = 2 V) hold is also possible. Therefore, this mode is effective when retaining the contents of data memory at an ultra-low current drain.

The μPD75402A STOP mode cannot be reset by interrupt request. It is reset only by RESET input.

(2) HALT mode

This mode stops the CPU operation clock. The system clock oscillator continues to oscillate. In this mode, the current drain is not reduced as much as the STOP mode, but this mode is effective when desiring to resume processing immediately by interrupt request and when desiring to perform intermittent operation, such as timer operation.

The HALT mode is reset by RESET input or interrupt request.

In either mode, the contents of the registers, flags, and data memory immediately before setting to the standby mode are retained. Because the states of the I/O port output latch and the output buffer are retained, the state of the I/O ports is preprocessed so that the current drain of the entire system is minimum.

Note 1.	Low current, low voltage operation is possible by switching the standby mode and CPU clock. However,
	in either case, the time described in paragraph 5.2.3 is necessary between operation of the PCC register
	and selection of the new clock and the start of operation by the new clock after switching. Therefore,
	when combining the clock switching function and standby mode, set the μPD75402A to the standby
	mode after the time required for switching has elapsed.
2.	When using the standby mode, ensure that the consumption current at the input/output is a minimum.	★
	In particular, do not leave the input port open : be sure to input a low-level or high-level signal.

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