SH7058 Datasheet, PDF (131/1130 Pages) Renesas Technology Corp – Renesas SuperHTM RISC engine

6.2 Resets
6.2.1 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 6.5, 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 6.5 Exception Source Detection and Exception Processing Start Timing
Conditions for Transition
to Reset State
Type
Power-on reset
Manual reset
RES
Low
High
High
WDT
Overflow
—
Power-on reset
Manual reset
CPU/MULT/
FPU/INTC
Initialized
Initialized
Initialized
Internal States
On-Chip
Peripheral
Modules
PFC, IO Port
Initialized
Initialized
Initialized
Not initialized
Not initialized Not initialized
6.2.2 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.
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-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.
Rev. 3.0, 09/04, page 90 of 1086