TMP88CU74F datasheet(37/132 Pages) TOSHIBA

37 / 132 page

TMP88CU74

2003-02-17

88CU74-37

1.6

Reset Circuit

The TMP88CU74 has four types of reset generation procedures: an external reset input, an

address trap reset output, a watchdog timer reset output and a system clock reset output. Table

1.6.1 shows on-chip hardware initialization by reset action.

The malfunction reset output circuit such as watchdog timer reset, address trap reset and

system clock reset is not initialized when power is turned on. The RESET pin can output level

“L” at the maximum 24/fc [s] (1.92

μs at 12.5 MHz) when power is turned on.

Table 1.6.1 Initializing Internal Status by Reset Action

On-chip Hardware

Initial Value

On-chip Hardwear

Initial Value

Program counter

(PC)

(FFFFEH to FFFFCH)

Stack pointer

(SP)

Not initialized

General-purpose registers

(W, A, B, C, D, E, H, L)

Not initialized

Prescaler and Divider of timing

generator

(RBS)

Jump status flag

(JF)

Watchdog timer

Enable

Zero flag

(ZF)

Not initialized

Carry flag

(CF)

Not initialized

Half carry flag

(HF)

Not initialized

Sign flag

(SF)

Not initialized

Overflow flag

(VF)

Not initialized

Interrupt master enable flag

(IMF)

Output latches of I/O ports

Refer to I/O port

circuitry

Interrupt individinal enable flags (EF)

Interrupt latchs

(IL)

Control registers

Refer to each of

control register

1.6.1

External Reset Input

The RESET pin contains a Schmitt trigger (hysteresis) with an internal pull-up resistor.

When the RESET pin is held at “L” level for at least 3 machine cycles (12/fc [s]) with the

power supply voltage within the operating voltage range and oscillation stable, a reset is

applied and the internal state is initialized.

When the RESET pin input goes high, the reset operation is released and the program

execution starts at the vector address stored at addresses FFFFC to FFFFEH.

Figure 1.6.1 Reset Circuit

VDD

Reset input

RESET

Sink open drain

Watchdog timer reset

Address trap reset

System clock reset

Malfunction reset

output circuit

2007-10-19

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