NEC PD75402A Manuale Utente
142
CHAPTER 7. STANDBY FUNCTION
7.1
STANDBY MODE SETTING AND OPERATION STATES
Table 7-1 Standby Mode Operation States
STOP Mode
HALT Mode
Setting instruction
HALT instruction
CPU clock
Φ
only stopped oscillator
(oscillation continues)
Operation
(IRQBT set at basic time interval)
(IRQBT set at basic time interval)
Operation possible
Output other than CPU clock
Φ
possible
Operation state
Operation stopped
INT2 : Operation possible
INT0 : Operation impossible
INT0 : Operation impossible
Interrupt request signal from operable
hardware enabled by interrupt enable
flag or RESET input.
hardware enabled by interrupt enable
flag or RESET input.
The STOP mode is set by STOP instruction and the HALT mode is set by HALT instruction. (The STOP instruction
and HALT instruction set bits 3 and 2 of the PCC respectively.)
Always write an NOP instruction after the STOP instruction or HALT instruction.
When the CPU operation clock is changed by means of the low-order two bits of the PCC, a time lag may be
generated between rewriting of the PCC and changing of the CPU clock. Therefore, when changing the operating
clock before the standby mode and when changing the CPU clock after standby mode reset, set the standby mode
after the number of machine cycles required to change the CPU clock has elapsed after the PCC is rewritten.
In the standby mode, the data of the general register, flags, mode registers, output latch, and all the other registers
which stop operating in the standby mode and the data memory is retained.
Notes are given below.
Note
1. When the STOP mode is set, the X1 pin is shorted internally to V
SS
(GND potential) to suppress clock
oscillator leakage. Therefore, do not use the STOP mode with systems that use an external clock.
2. STOP mode reset by interrupt request differs as follows for the
µ
PD75402A and the evachip installed
on the evaluation board:
•
µ
PD75402A
••••••
STOP mode not reset by interrupt request.
•
Evachip
••••••••••••••
STOP mode reset by interrupt request.
To eliminate the affect of this difference, disable all interrupt requests before setting the
µ
PD75402A
to the STOP mode.
3. From the standpoint that an interrupt request signal is used to reset the HALT mode, when there is an
interrupt source which sets both the interrupt request flag and interrupt enable flag (1), the HALT mode,
even if entered, is immediately reset.
Reset signal
RESET input
STOP instruction
Clock oscillation stopped
Operation stopped
Operation possible only when external
SCK input selected as serial clock
SCK input selected as serial clock
Operation stopped
Clock generator
Basic interval timer
Serial interface
Clock output circuit
External interrupt
CPU