25

µPD780921, 780922, 780923, 780924

7. EXTERNAL DEVICE EXPANSION FUNCTION

The external device expansion function is used to connect external devices to areas other than the internal ROM, RAM

and SFR.

Ports 4 to 6 are used for connection with external devices.

8. STANDBY FUNCTIONS

There are the following two standby functions to reduce the current consumption.

• HALT mode

: The CPU operating clock is stopped. The average current consumption can be reduced by intermittent

operation in combination with the normal operating mode.

• STOP mode

: The system clock oscillation is stopped. The whole operation by the system clock is stopped, so that

the system operates with ultra-low power dissipation.

Figure 8-1. Standby Functions

System Clock Operation

STOP Instruction

Interrupt

Request

STOP Mode

(System clock oscillation

is stopped)

HALT Instruction

Interrupt

Request

HALT Mode

(Clock supply to CPU is stopped,

and oscillation is maintained)

9. RESET FUNCTIONS

There are the following two reset methods.

• External reset by RESET input.

• Internal reset by watchdog timer runaway time detection