NEC PD78214 - Manual (Page 411)

382
µ
PD78214 Sub-Series
14.4 STOP MODE
14.4.1 Specifying STOP Mode and Operation States in STOP Mode
The system enters STOP mode when the STP bit of the STBC register is set to 1.
The STBC register can be written only with a specified 8-bit data write instruction. To specify STOP mode, execute
the “MOV STBC, #02H” instruction.
Table 14-4 Operation States in STOP Mode
Clock oscillator
Internal system clock
CPU
I/O lines
Peripheral functions
Internal RAM
AD0-AD7
Bus lines A8-A15
A16-A19
RD, WR output
ASTB output
Operating
Operating
Stopped
Same as before entering STOP mode
Stopped Note
Contents maintained
High-impedance
States maintained
Low
High
Low
Note The A/D converter stops, but its current dissipation is not reduced if the CS bit of the A/D converter mode register (ADM) is set.
Cautions 1. In STOP mode, the X1 pin is internally short-circuited to V
SS
(ground potential) to prevent current leakage from the clock
oscillator circuit. STOP mode must not, therefore, be specified for a system using an external clock.
2. Reset the CS bit for the A/D converter.
3. The system enters STOP mode even if an NMI request is being held when STOP mode is specified. When using an NMI request
to release STOP mode, input the NMI signal again.
14.4.2 Releasing STOP Mode
STOP mode can be released by inputting an NMI or RESET signal.
(1) Releasing STOP mode by NMI input
(a) Operation
The oscillator restarts when an effective edge, specified with the external interrupt mode register
(INTM0), is detected at the NMI pin. Then, STOP mode is released after the specified time, required to
allow the oscillation to settle, has elapsed.
Once STOP mode has been released, processing branches to the NMI service program if the NMIS bit of
the interrupt status register (IST) is set to 0. If the NMIS bit is set to 1 (for example, when STOP mode
is specified in the NMI interrupt service program), processing is resumed from the instruction subsequent
to that which specified STOP mode. Processing then branches to the NMI interrupt service program when
the NMIS bit is set to 0 (for example, with a RETI instruction).
(b) Oscillation settling time
The oscillator restarts when an effective, edge specified with the external interrupt mode register
(INTM0), is detected at the NMI pin. Then, when the input level of the NMI signal returns to its original
level, the oscillation settling time counter starts counting. When the 16-bit counter overflows (in 11 ms
when f
XX
= 12 MHz), the internal system clock is started. The system therefore waits, from the detection
of the effective edge to the start of the internal clock, a total time equal to the high- or low-level width of
the NMI signal after detecting the effective edge and the time needed for the 16-bit oscillation settling time
counter to overflow.