M306H7MG-XXXFP Datasheet, PDF (310/329 Pages) Renesas Technology Corp – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER with DATA ACQUISITION CONTROLLER

M306H7MG-XXXFP/MC-XXXFP/FGFP
19. USAGE NOTES
19.3.2 Setting the SP
Set any value in the SP (USP, ISP) before accepting an interrupt. The SP (USP, ISP) is cleared to ‘000016’ after
reset. Therefore, if an interrupt is accepted before setting any value in the SP (USP, ISP), the program may go
out of control.
Especially when using NMI interrupt, set a value in the ISP at the beginning of the program. For the first and
only the first instruction after reset, all interrupts including NMI interrupt are disabled.
19.3.3 The NMI Interrupt
(1) The NMI interrupt cannot be disabled. If this interrupt is unused, connect the NMI pin to VCC via a
resistor (pull-up).
(2) The input level of the NMI pin can be read by accessing the P8 register’s P8_5 bit. Note that the P8_5
bit can only be read when determining the pin level in NMI interrupt routine.
(3) Stop mode cannot be entered into while input on the NMI pin is low. This is because while input on the
NMI pin is low the CM1 register’s CM10 bit is fixed to “0”.
(4) Do not go to wait mode while input on the NMI pin is low. This is because when input on the NMI pin
goes low, the CPU stops but CPU clock remains active; therefore, the current consumption in the chip
does not drop. In this case, normal condition is restored by an interrupt generated thereafter.
(5) The low and high level durations of the input signal to the NMI pin must each be 2 CPU clock cycles +
300 ns or more.
19.3.4 Changing the Interrupt Generate Factor
If the interrupt generate factor is changed, the IR bit in the interrupt control register for the changed interrupt
may inadvertently be set to “1” (interrupt requested). If you changed the interrupt generate factor for an
interrupt that needs to be used, be sure to clear the IR bit for that interrupt to “0” (interrupt not requested).
“Changing the interrupt generate factor” referred to here means any act of changing the source, polarity or
timing of the interrupt assigned to each software interrupt number. Therefore, if a mode change of any
peripheral function involves changing the generate factor, polarity or timing of an interrupt, be sure to clear the
IR bit for that interrupt to “0” (interrupt not requested) after making such changes.
Refer to the description of each peripheral function for details about the interrupts from peripheral
functions.
Figure 19.1 shows the procedure for changing the interrupt generate factor.
Rev.2.10 Oct 25, 2006 Page 310 of 326
REJ03B0152-0210