3-1
MSM66573 Family User's Manual
Chapter 3 CPU Control Functions
3
Figure 3-1 Transition Diagram of CPU Operating States
3.
CPU Control Functions
3.1
Overview
The MSM66573 family has two CPU control functions, a standby function and a reset
function.
The standby function consists of the three functions of HALT mode, HOLD mode, and
STOP mode. These functions can be used to reduce the amount of power consumed during
operation. The HOLD mode has a bus release function, and the STOP mode has a quick
activating STOP mode in which the main clock continues oscillation.
The reset function is activated by the
RES 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 MSM66573 family has three types of standby functions.
HALT mode: activated by software, clock supply to CPU is terminated
HOLD mode: activated by hardware, 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
HOLD mode
High-speed
HALT mode
Low-speed
HOLD mode
Low-speed
HALT mode
High-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)
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."
HOLD input = 1
(when HOLD is enabled)
STP = 1
HOLD input = 0
HLT = 1
Subclock
(XT) selection
Main clock
(OSC) selection
HLT = 1
HOLD input = 1
(When HOLD is enabled)
HOLD input = 0
STP = 1
Interrupt
generated
Low-speed STOP mode
(Terminate main clock oscillation: OSCS = 1)
(Operate main clock oscillation: OSCS = 0)
Interrupt
generated
Interrupt
generated
Interrupt
generated