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ML66525 Family User’s Manual
Chapter 3
CPU Control Functions
3 - 1
3.
CPU Control Functions
3.1
Overview
The ML66525 family has two CPU control functions, a standby function and a reset function.
The standby function consists of the two functions of HALT mode and STOP mode.
These
functions can be used to reduce the amount of power consumed during operation.
The STOP
mode has a quick activating STOP mode in which the main clock continues oscillation.
The reset function is activated by the RESn signal input, BRK (break) instruction execution, or
execution of an invalid instruction (opcode trap).
In addition, reset is also activated by
overflow of the watchdog timer.
Reset can minimize the effect of program errors on the
system.
3.2
Standby Functions
The ML66525 family has two types of standby functions.
HALT mode: activated by software, clock supply to CPU is terminated
STOP mode: activated by software, clock supply to CPU and internal peripheral modules is
terminated
Corresponding to each of dual clocks, each of these functions has a high-speed and low-speed
mode.
Figure 3-1 shows a transition diagram of the CPU operating states.
Table 3-1 lists a summary
of the standby modes.
High-speed
HALT mode
High-speed main
clock (OSC) operation
Initial state when RESET
(Notes)
Oscillation operation or termination is for the main clock (OSC) only.
The subclock (XT) is not terminated.
The initial value of OSCS (bit 3 of SBYCON) is “1”.
Stopping the main clock (OSC) with OSCS is effective when P9_0/VBUSIN is at a “L” level
for input; alternatively, when P9_0/VBUSIN is at a “H” level for input and the USB control
function is in the power down state (refer to Chapter 17).
STP = 1
HLT = 1
Subclock
(XT) selection
Main clock
(OSC) selection
HLT = 1
Interrupt
generated
STP = 1
Low-speed
HALT mode
Interrupt
generated
Interrupt
generated
Interrupt
generated
High-speed STOP mode
(Terminate main clock oscillation: OSCS = 1)
(Operate main clock oscillation: OSCS
= 0)
Low-speed STOP mode
(Terminate main clock oscillation: OSCS = 1)
(Operate main clock oscillation: OSCS = 0)
Low-speed subclock (XT) operation
(Terminate main clock oscillation: OSCS = 1)
(Operate main clock oscillation: OSCS = 0)
Figure 3-1
Transition Diagram of CPU Operating States