MC68LC302 Datasheet, PDF (29/169 Pages) Motorola, Inc – Low Power Integrated Multiprotocol Processor Reference Manual

Configuration, Clocking, Low Power Modes, and Internal Memory Map
PLL output clock that provides the IMP system clock. Switching between the NORMAL and
SLOW_GO modes is achieved by changing the DF3–0 field in the IOMCR register to a non-
zero value. The IMP PLL will not lose lock when the DF3–0 field in the IOMCR register is
changed.
2.4.4.2.2 Entering the STOP/ DOZE/ STAND_BY Mode. Entering the STOP/ DOZE/
STAND_BY mode is achieved by the 68000 core executing the following code:
nop
move.b
stop
nop
*+6(PC),$000000FB
#$xxxx
;copy STOP operand high byte to addr 000000fb
;xxxx -> SR
This code is position independent. The core must be in the supervisor state to execute the
STOP instruction, therefore the write to $000000FB must be done in the supervisor state
(function code 5, supervisor data). The core trace exception should be disabled, otherwise
the low power control will not enter the STOP mode.
To guarantee supervisor state and trace exceptions disabled, this code should be part of a
TRAP routine. Upon entering the trap routine, examine the stacked status register. If it indi-
cates the supervisor state, then execute this code to enter STOP mode. If not supervisor,
do NOT execute this code (could perform some application-specific error):
TRAP_x
NO_STOP
btst.b
beq.s
nop
move.b
stop
nop
rte
...
#5,(SP)
NO_STOP
*+6(PC),$000000FB
#$xxxx
; supervisor?
; flush execution, bus pipes
;copy STOP operand high byte to addr 000000fb
; xxxx -> SR
; error routine?
NOTE
The RI/PB9, DTE/PB10, and periodic interrupt timer timeout in-
terrupts conditions will generate level 4 interrupts. The user
should set the 68000 interrupt mask register to the appropriate
level before executing this code.
IMP’s low power control logic will:
1. Detect the write cycle.
2. Check if bit 5 = 1 (supervisor space) (if it is 0, the low power request will be ignored).
3. Sample the interrupt mask bits (bits 0–2). If during this process of stopping the clocks
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MC68LC302 REFERENCE MANUAL
MOTOROLA