UPD780949 datasheet(39/69 Pages) RENESAS

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µPD780949(A)

External Device Expansion Functions

The external device expansion functions connect external devices to areas other than the internal

ROM, RAM and SFR. External devices connection uses ports 4 to 6.

The external device expansion function has the following mode:

• Multiplexed bus mode:

External devices are connected by using a time-division

multiplexed address /data bus. This mode is useful for reducing

the number of ports used when external devices are connected.

Note:

Current consumption is reduced by shutting off the main system clock.

If the CPU is operating on subsystemclock, shut off the main system clock by setting MCC.

Caution:

When switching on the main system clock again after the subsystem clock has been used

with the main system clock stopped, be sure to provide enough time for the generation

to be stable with the program first.

Figure 9-1: Standby Function

Standby Function

The standby function intends to reduce current consumption. It has the following two modes:

• HALT mode:

In this mode, the CPU operation clock is stopped. The average current consump-

tion can be reduced by intermittent operation by combining this mode with the

normal operation mode.

• STOP mode:

In this mode, oscillation of the main system clock is stopped. All the operations

performed on the main system clock are suspended, and only the subsystem

clock is used for extremely small power consumption.

EEPROM Function

The µPD780949 incorporates not only a 2016 byte x 8-bit RAM but also 256 byte x 8-bit EEPROM

(Electrically Erasable PROM) as data memory.

EEPROM, unlike static RAM, can retain its contents when the power is turned off. Unlike EPROM,

it‘s contents can electrically be erased without using ultraviolet rays. EEPROM is manipulated by

8-bit memory manipulation instructions.

10. Reset Function

There are the following two reset methods.

• External reset input by RESET pin

• Internal reset by watchdog timer runaway time detection

Main System Clock Operation

Subsystem Clock Operation

Note

Interrupt

request

STOP

instruction

STOP Mode

(Oscillation of the main system

clock is stopped.)

Interrupt

request

Interrupt

request

HALT instruction

HALT Mode

(Supply of clock to CPU is

stopped although clock

is generated.)

HALT instruction

HALT Mode

Note

(Supply of clock to CPU is

stopped although clock

is generated.)

CSS = 1

CSS = 0

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