7480 데이터 시트보기 (PDF) - Renesas Electronics

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7480

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

Renesas Electronics 

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MITSUBISHI MICROCOMPUTERS

7480/7481 GROUP

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

STP/WIT Instruction Control

The STP instruction and the WIT instruction can be enabled or

disabled selectively by using the STP instruction operation control

register. To cope with a program runaway after reset, the STP in-

struction and the WIT instruction are disabled in the initial status.

The STP and WIT instructions can be set as enable/disable only

by writing to the STP instruction operation control register twice

successively so as not to stop the oscillation clock even if a write

data error is caused by program runaway. Figure 41 shows a

structure of the STP instruction operation control register.

b7

b0

STP instruction operation control register

(STPCON: address 00DE 16)

STP instruction and WIT instruction enable/disable selection bit (Note)

0 : STP/WIT instruction enabled

1 : STP/WIT instruction disabled

Not used (“0” at read)

Note : The STP instruction and the WIT instruction are disabled in the initial status. When using these

instructions, set bit 0 of the STP instruction operation control register to “1”, then set this bit to “0”.

(Writing twice successively)

When not using the STP and WIT instructions, set this bit to “1” either once or twice.

Fig. 41 Structure of STP instruction operation control register

Explanation of STP Instruction Operation

Control Register

The STP instruction operation control register will be enabled by

writing data to the same address twice successively. If data is not

written in continuous form, the written data is not valid but the pre-

vious value is held.

If an interrupt is received while the same data is written twice,

there is a possibility that the write instruction in the interrupt rou-

tine may be executed. For this reason, rewriting is required after

interrupt disable. Figure 42 shows a reference example of data re-

writing.

qSTP/WIT instruction enable

•

•

•

SEI

LDM #01H, 0DEH

LDM #00H, 0DEH

CLI

Interrupt

disable in

this period

•

•

• Use only in interrupt enable status

Fig. 42 Reference example of data rewriting

qSTP/WIT instruction disable

•

•

•

SEI

LDM #01H, 0DEH

LDM #01H, 0DEH

CLI

Interrupt

disable in

this period

•

•

•

Use only in interrupt enable status

40

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