SH7670 Datasheet, PDF (140/1292 Pages) Renesas Technology Corp – 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7670 Series

Section 5 Exception Handling
5.2.3 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-tcyc
(unfixed) 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.
Rev. 1.00 Nov. 14, 2007 Page 114 of 1262
REJ09B0437-0100