NEC PD750008 - Manual (Page 240)

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µPD750008 USER'S MANUAL
7.4 SELECTION OF A MASK OPTION
For the standby function of the µPD750008, either of the following two values can be selected by a mask
option as the wait time during which the start of oscillation deferred from the generation of a RESET signal:
<1> 2 17 /f
X
(21.8 ms at 6.00 MHz, 31.3 ms at 4.19 MHz)
<2> 2 15 /f
X
(5.46 ms at 6.00 MHz, 7.81 ms at 4.19 MHz)
However, the µPD75P0016 dose not have a mask option and its wait time is fixed to 2 15 /f
X
.
7.5 APPLICATIONS OF THE STANDBY MODES
When the standby modes are used, the following steps are used.
<1> Detect a standby mode setting factor such as power removal on an interrupt input or port input. (INT4
is useful for power removal detection.)
<2> Configure I/O ports for minimum current drain.
<3> Specify interrupts for releasing a standby mode. (INT4 is useful. All interrupt enable flags not used
for release are to be cleared.)
<4> Specify an operation to be performed after release. (IME is to be manipulated according to whether
interrupt processing is performed or not.)
<5> Specify a CPU clock to be used after release. (If the CPU clock is changed, required machine cycles
must elapse before the standby mode is set.)
<6> Select a wait time to be used when a standby mode is released.
<7> Set a standby mode using a STOP or HALT instruction.
A standby mode when combined with the system clock switch function enables a lower power consumption
and lower-voltage operation.
(1) Application of the STOP mode (at f
X
= 4.19 MHz)
<Use of the STOP mode under the following conditions>
• The STOP mode is set on the falling edge of INT4, and is released on the rising edge of INT4. (INTBT
is not used.)
• All I/O ports have a high impedance.
• The INT0 and INTT0 interrupts are used for the program, but are not used to release the STOP mode.
• After the STOP mode is released, interrupts are enabled.
• After the STOP mode is released, the lowest-speed CPU clock is used for operation. Then, the CPU
clock is changed to the high-speed one after 250 ms.
• A wait time used when the STOP mode is released is about 31.3 ms.
• After the STOP mode is released, another wait time of 31.3 ms is used for stable power supply operation.
The P00/INT4 pin is checked twice to remove chattering.