Datasheet

System Integration Module (SIM)
Low-Power Modes
MC68HC908QY4•MC68HC908QT4•MC68HC908QY2•MC68HC908QT2•MC68HC908QY1•MC68HC908QT1
MOTOROLA System Integration Module (SIM) 95
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7.8.2 Stop Mode
In stop mode, the SIM counter is reset and the system clocks are
disabled. An interrupt request from a module can cause an exit from stop
mode. Stacking for interrupts begins after the selected stop recovery
time has elapsed. Reset or break also causes an exit from stop mode.
The SIM disables the oscillator signals (BUSCLKX2 and BUSCLKX4) in
stop mode, stopping the CPU and peripherals. Stop recovery time is
selectable using the SSREC bit in the configuration register 1
(CONFIG1). If SSREC is set, stop recovery is reduced from the normal
delay of 4096 BUSCLKX4 cycles down to 32. This is ideal for the internal
oscillator, RC oscillator, and external oscillator options which do not
require long start-up times from stop mode.
NOTE: External crystal applications should use the full stop recovery time by
clearing the SSREC bit.
The SIM counter is held in reset from the execution of the STOP
instruction until the beginning of stop recovery. It is then used to time
the recovery period. Figure 7-18 shows stop mode entry timing and
Figure 7-19 shows the stop mode recovery time from interrupt or break
NOTE: To minimize stop current, all pins configured as inputs should be driven
to a logic 1 or logic 0.
Figure 7-18. Stop Mode Entry Timing
STOP ADDR + 1 SAME SAMEADDRESS BUS
DATA BUS
PREVIOUS DATA NEXT OPCODE SAME
STOP ADDR
SAME
R/W
CPUSTOP
NOTE: Previous data can be operand data or the STOP opcode, depending on the last
instruction.