Panasonic F77G Transition to Standby Modes, Processing inside parentheses is handled by hardware

Models: F77G MN101C77C

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Chapter 2 CPU Basics

2-4-4 Transition to STANDBY Modes

The program initiates transitions from a CPU operating mode to the corresponding STANDBY (HALT/ STOP) modes by specifying the new mode in the CPU mode control register (CPUM). Interrupts initiate the return to the former CPU operating mode.

Before initiating a transition to a STANDBY mode, however, the program must

(1)Set the maskable interrupt enable flag (MIE) in the processor status word (PSW) to '0' to disable all maskable interrupts temporarily.

(2)Set the interrupt enable flags (xxxIE) in the interrupt control registers (xxxICR) to '1' or '0' to specify which interrupts do and do not initiate the return from the STANDBY mode. Set MIE '1' to enable those maskable interrupts.

NORMAL/SLOW

mode

Disable all interrupts

Clear MIE flag in the PSW and all interrupt enable flags (xxx IE) in the maskable interrupt control register.

Enable interrupt which

will trigger return

Set HALT/STOP

mode

Set the xxx IE of the return factor, and set MIE flag in the PSW.

HALT/STOP

 

Watchdog timer

 

mode

 

(HALT: stop counting

)

 

 

 

STOP: reset

 

Processing inside parentheses () is handled by hardware.

When returning from STOP (mode, wait for oscillation to)

stabilize

Return factor interrupt occured

 

 

Watchdog timer

NORMAL/SLOW

 

(HALT: restarts counting)

 

mode

 

STOP: enabled

Interrupt acceptance cycle

Figure 2-4-3 Transition to/from STANDBY Mode

If the interrupt is enabled but interrupt priority level of the interrupt to be used is not equal to or higher than the mask level in PSW before transition to HALT or STOP mode, it is impos- sible to return to CPU operation mode by maskable interrupt.

Standby Functions

II - 23

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Panasonic F77G, MN101C77C user manual Transition to Standby Modes, Processing inside parentheses is handled by hardware