HD64F7047 datasheet(101/764 Pages) RENESAS

101 / 764 page

Rev. 2.00, 09/04, page 61 of 720

5.2

Resets

5.2.1

Types of Reset

Resets have the highest priority of any exception source. There are two types of resets: manual

resets and power-on resets. As table 5.5 shows, both types of resets initialize the internal status of

the CPU. In power-on resets, all registers of the on-chip peripheral modules are initialized; in

manual resets, they are not.

Table 5.5

Reset Status

Conditions for Transition

to Reset Status

Internal Status

Type

RES

WDT

Overflow

MRES

CPU/INTC

On-Chip

Peripheral

Module

PFC, IO Port

Low



Initialized

Power-on reset

High

Overflow

High

Initialized

Not initialized

Manual reset

High



Low

Initialized

Not initialized Not initialized

5.2.2

Power-On Reset

Power-On Reset by

RES Pin: When the RES pin is driven low, the LSI becomes to be a power-

on reset state. To reliably reset the LSI, the

RES pin should be kept at low for at least the duration

of the oscillation settling time when applying power or when in standby mode (when the clock

circuit is halted) or at least 20 t

cyc when the clock circuit is running. During power-on reset, CPU

internal status and all registers of on-chip peripheral modules are initialized. See Appendix B, Pin

States, for the status of individual pins during the power-on reset status.

In the power-on reset status, 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 will then operate 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 (B'1111).

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

program begins executing.

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

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