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Chapter 9
Clock Generator
Preliminary User’s Manual U15839EE1V0UM00
9.4.4 HALT
mode
In this mode, the CPU clock is stopped, though the clock generators (oscillator, SSCG and PLL synthe-
sizer) continue to operate for supplying clock signals to other peripheral function circuits.
Setting the HALT mode when the CPU is idle reduces the total system power consumption.
In the HALT mode, program execution is stopped but the contents of all registers and internal RAM prior
are retained as is.
On-chip peripheral hardware irrelevant to the CPU instruction execution also continues to operate. The
state of the various hardware units in the HALT mode is tabulated below.
Table 9-4:
Operating states in HALT mode
Remark:
Even after the HALT instruction is executed, instruction fetch operations continue until the
internal instruction pre-fetch queue is full. After the queue becomes full, the CPU stops with
the items set as tabulated above.
HALT mode release:
The HALT mode can be released by a non-maskable interrupt request, an unmasked maskable inter-
rupt request, or RESET signal input.
(1)
Release by interrupt request
The HALT mode is released unconditionally by an unmasked maskable interrupt request
regardless of its priority level. However, if the HALT mode is entered during execution of an
interrupt handler, the operation differs on interrupt priority levels as follows:
(a) If an interrupt request less prioritized than the currently serviced interrupt request is gener-
ated, the HALT mode is released but the interrupt is not acknowledged. The interrupt request
itself is retained.
(b) If an interrupt request (including a non-maskable one) prioritized than the currently serviced
interrupt request is generated, the interrupt request is acknowledged along with the HALT
mode release.
Items
Operation
Clock generator
Operating
SSCG/PLL
Operating
Internal system clock
Operating
WT, WDT clock
Operating
CPU
Stopped (but CPU clock still operates)
I/O line
Unchanged
Peripheral function
Operating
TMC calibration input
Main Clock available
Internal data
Retains all internal data before entering HALT mode, such
as CPU registers, status, data, and on-chip RAM.
CLKOUT pin
Clock output (when not inhibited by port setting)
D[15:0], A[23:0], RD, WR1/
WR0, CS[0], CS[3:4], WAIT
Operates
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