SH7058 Datasheet, PDF (990/1130 Pages) Renesas Technology Corp – Renesas SuperHTM RISC engine

25.2.4 Notes on Register Access
The method of writing to system control register 2 (SYSCR2) is different from that of ordinary
registers to prevent inadvertent rewriting.
Be certain to use a word transfer instruction when writing data to SYSCR2. Data cannot be written
by a byte transfer instruction. As shown in figure 25.1, set the upper byte to H'3C and transfer data
using the lower byte as write data.
Data can be read by the same method as for ordinary registers.
SYSCR2 is allocated to address H'FFFFF70A. Always use a byte transfer instruction to read data.
When writing to SYSCR2
15
Address: H'FFFFF70A
H'3C
87
0
Write data
Figure 25.1 Writing to SYSCR2
25.3 Hardware Standby Mode
25.3.1 Transition to Hardware Standby Mode
The chip enters hardware standby mode when the HSTBY and RES pins go low. The mode pin
should be set according to the pin settings described in section 4, Operating Modes. If other
settings are applied to the mode pin, operation cannot be guaranteed. Hardware standby mode
reduces power consumption drastically by halting all SH7058 functions. As the transition to
hardware standby mode is made by means of external pin input, the transition is made
asynchronously, regardless of the current state of the SH7058, and therefore the chip state prior to
the transition is not preserved. However, on-chip RAM data is retained as long as the specified
voltage is supplied. To retain on-chip RAM data, clear the RAM enable bit (RAME) to 0 in the
system control register 1 (SYSCR1) before driving the HSTBY pin low.
25.3.2 Canceling Hardware Standby Mode
Hardware standby mode is canceled by means of the HSTBY pin and RES pin. When HSTBY is
driven high while RES is low, the clock oscillator starts running. The RES pin should be held low
long enough for clock oscillation to stabilize. When RES is driven high, power-on reset exception
processing is started and a transition is made to the program execution state.
Rev. 3.0, 09/04, page 949 of 1086