
ML66517 Family User’s Manual
Chapter 3
CPU Control Functions
3 – 4
(2) Standby control register (SBYCON)
The standby control register (SBYCON) is an 8-bit register that sets the standby mode and the CPU
operating clock (CPUCLK).
The program can read from and write to SBYCON.
At reset (due to a
RES input, BRK instruction execution, watchdog timer overflow, or opcode trap),
SBYCON is 08H.
Figure 3-2 shows the configuration of SBYCON.
[Description of each bit]
STP (bit 0)
Setting the stop code acceptor (STPACP) to “1”, and then setting STP to “1” will change the mode to the
STOP mode. When an interrupt is generated or the
RES input causes a reset, STP is reset to “0” and the
STOP mode is released.
HLT (bit 1)
Setting HLT to “1” changes the mode to the HALT mode. When an interrupt is generated, the
RES input
causes a reset, or overflow of the watchdog timer causes a reset, HLT is reset to “0” and the HALT mode
is released.
FLT (bit 2)
Setting FLT to “1” will cause the output ports (all pins set to output mode) to go to a high impedance
state when the STOP mode is entered.
At the input ports, a circuit operates to prevent current flow between the power supply and GND, even if
the inputs are left unconnected. Therefore, it is not necessary to fix the input pin levels during the STOP
mode.
However, if the following pins are used as inputs (regardless of whether they are primary or
secondary functions), the circuit to prevent current flow will not operate. Thus, to prevent undefined input
states, use either pull-up or pull-down resistors (to fix the input levels) during the STOP mode.
P6_0 to P6_3: External interrupt pins (EXINT0 to EXINT3)
Using the above pins as secondary function inputs, even if the STOP mode is entered with FLT set (“1”),
the STOP mode can be released by an external interrupt input. For details, refer to Section 3.2.4,
“Operation of Each Standby Mode,” (2) STOP Mode.
OSCS (bit 3)
During the STOP mode, OSCS specifies whether to terminate or continue oscillation of the main clock
(OSCCLK).
OST0, OST1 (bits 4 and 5)
In the case when an interrupt causes the STOP mode to be released, OST0 and OST1 specify the
oscillation stabilization time from the oscillation start of the main clock (OSCCLK) until clock supply to
the CPU. During the STOP mode, even if oscillation of the main clock (OSCCLK) is not terminated, the
settings of these bits are valid.
[Note]
Do not set OST0 and OST1 to “1”, in the case of changing to the operation mode in which oscillation of the
main clock (OSCCLK) is terminated.
For the Flash ROM version, set the oscillation stabilization time of 50
s or more (tentative) when the
STOP mode (only when oscillation of the main clock is terminated) is released.