SH-2 datasheet(91/919 Pages) RENESAS

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5.2

Resets

5.2.1

Types of Reset

A reset is the highest-priority exception processing source. There are two kinds of reset, power-on

and manual. As shown in table 5.5, the CPU state is initialized in both a power-on reset and a

manual reset. On-chip peripheral module registers are also initialized by a power-on reset, but not

by a manual reset.

Table 5.5

Exception Source Detection and Exception Processing Start Timing

Conditions for Transition

to Reset State

Internal States

Type

RES

WDT

Overflow

CPU/MULT/

FPU/INTC

On-Chip

Peripheral

Modules

PFC, IO Port

Power-on reset

Low

—

Initialized

High

Power-on reset

Initialized

Not initialized

Manual reset

High

Manual reset

Initialized

Not initialized

5.2.2

Power-On Reset

Power-On Reset by Means of

RES Pin: When the RES pin is driven low, the chip enters the

power-on reset state. To reliably reset the chip, the

RES pin should be kept at the low level for at

least the duration of the oscillation settling time at power-on or when in standby mode (when the

clock is halted), or at least 20 t

cyc when the clock is running. In the power-on reset state, the CPU’s

internal state and all the on-chip peripheral module registers are initialized. See Appendix B, Pin

States, for the state of individual pins in the power-on reset state.

In the power-on reset state, power-on reset exception processing starts when the

RES pin is first

driven low for a set period of time and then returned to high. The CPU operates as follows:

1. The initial value (execution start address) of the program counter (PC) is fetched from the

exception processing vector table.

2. The initial value of the stack pointer (SP) is fetched from the exception processing vector table.

3. The vector base register (VBR) is cleared to H'00000000 and the interrupt mask bits (I3 to I0)

of the status register (SR) are set to H'F (1111).

4. The values fetched from the exception processing vector table are set in the PC and SP, and the

program begins executing.

Be certain to always perform power-on reset processing when turning the system power on.

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