M34286G2GP datasheet(17/66 Pages) RENESAS

17 / 66 page

Rev.1.00

Aug 06, 2008

page 17 of 64

REJ03B0251-0100

4286 Group

LOGIC OPERATION FUNCTION

The 4286 Group has the 4-bit logic operation function. The logic

operation between the contents of register A and the low-order 4

bits of register E is performed and its result is stored in register A.

Each logic operation can be selected by setting logic operation

selection register LO.

Set the contents of this register through register A with the TLOA

instruction. The logic operation selected by register LO is

executed with the LGOP instruction.

Table 5 shows the logic operation selection register LO.

Table 5 Logic operation selection register LO

Note: “W” represents write enabled.

WATCHDOG TIMER

Watchdog timer provides a method to reset and restart the system

when a program runs wild. Watchdog timer consists of 14-bit

timer (WDT) and watchdog timer flags (WDF1, WDF2).

Watchdog timer downcounts the instruction clock (INSTCK) as

the count source immediately after system is released from reset.

When the timer WDT count value becomes 000016 and underflow

occurs, the WDF1 flag is set to “1.” Then, when the WRST

instruction is not executed before the timer WDT counts 16383,

WDF2 flag is set to “1” and internal reset signal is generated and

system reset is performed.

Execute the WRST instruction at period of 16383 machine cycle

or less to keep the microcomputer operation normal.

Timer WDT is also used for generation of oscillation stabilization

time. When system is returned from reset and from RAM back-

up mode by key-input, software starts after the stabilization

oscillation time until timer WDT downcounts to 3E0016 elapses.

Fig. 18 Watchdog timer function

Value of timer WDT

WDF2 flag

WRST

instruction

execution

System

reset

Return

3E0016

0000 16

WDF1 flag

3FFF16

System

reset

Software start

POF

instruction

execution

Internal reset signal

“1”

“0”

“1”

“0”

“H”

“L”

at reset : 002

at RAM back-up : 002

LO1

LO0

LO1

LO0

Logic operation selection bits

Logic operation selection register LO

Logic operation function

Exclusive logic OR operation (XOR)

OR operation (OR)

AND operation (AND)

Not available

•

Watchdog timer

Be sure that the timing to execute the WRST instruction in

order to operate WDT efficiently.

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