SH7243 datasheet(132/1726 Pages) RENESAS

132 / 1726 page

Section 5 Exception Handling

Rev. 1.00 Jun. 26, 2008 Page 102 of 1692

REJ09B0393-0100

5.2.2

Power-On Reset

(1)

Power-On Reset by Means of

RES Pin

When the

RES pin is driven low, this LSI enters the power-on reset state. To reliably reset this

LSI, the

RES pin should be kept at the low level for the duration of the oscillation settling time at

power-on or when in software 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 internal state of the CPU and all the on-chip

peripheral module registers are initialized. See appendix A, Pin States, for the status of individual

pins during the power-on reset state.

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

RES pin is first

driven low for a fixed period 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 handling vector table.

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

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

I0) of the status register (SR) are initialized to H'F (B'1111), and the BO and CS bits are

initialized. The BN bit in IBNR of the INTC is also initialized to 0.

4. The values fetched from the exception handling 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.

(2)

Power-On Reset by Means of H-UDI Reset Assert Command

When the H-UDI reset assert command is set, this LSI enters the power-on reset state. Power-on

reset by means of an H-UDI reset assert command is equivalent to power-on reset by means of the

RES pin. Setting the H-UDI reset negate command cancels the power-on reset state. The time

required between an H-UDI reset assert command and H-UDI reset negate command is the same

as the time to keep the

RES pin low to initiate a power-on reset. In the power-on reset state

generated by an H-UDI reset assert command, setting the H-UDI reset negate command starts

power-on reset exception handling. The CPU operates in the same way as when a power-on reset

was caused by the

RES pin.

SH7243 Datasheet(PDF) 132 Page - Renesas Technology Corp