MC68HC05F8 Datasheet, PDF (101/126 Pages) Motorola, Inc – High-density complementary metal oxide semiconductor(HCMOS) microcontroller unit

Freescale Semiconductor, Inc.
11
LOW POWER MODES
The STOP and WAIT instructions have different effects on the Timers, Serial Peripheral Interface
(SPI), and DTMF/Melody Generator (DMG). These are discussed in the following paragraphs.
11.1
Stop Mode
When the processor executes the STOP instruction, the internal clock is turned off. This halts all
internal CPU processing, including the operation of the Programmable Timer, SPI and DMG. The
I bit in the Condition Code register is cleared to enable external interrupts (INTE1, INTE2 and
KEYE bits are unaltered). All registers and memory remain unaltered, and all input/output lines
remain unchanged.
The MCU is exited from Stop mode by an interrupt on either IRQ1 or IRQ2, or any keyboard
interrupts, or any resets (logic low on RESET pin or a power-on reset). On exit from Stop mode,
the program counter is loaded with the corresponding interrupt vector (see Table 5-1). The effects
of the Stop mode on each of the MCU peripheral systems are described separately.
11.1.1 Timer A during Stop Mode
When Stop mode is entered, the timer A (programmable timer) counter stops counting (the
internal processor clock is stopped) and remains at that particular count value until the Stop mode
is exited. If the exit was caused by reset, the counter is forced to $FFFC. If the Stop mode is exited
by an interrupt (IRQ1, IRQ2, or keyboard interrupt), the counter resumes counting from the value
when it entered the Stop mode. Another feature of the programmable timer in the Stop mode is,
that if at least one valid input capture edge occurs at the TCAP pin, the input capture detect
circuitry is armed. This action does not set any timer flags or “wake up” the MCU, but when the
MCU does “wake up” there will be an active input capture flag (and data) from that first valid edge
which occurred during the Stop mode. Notice that an exit by a reset will reset the entire MCU and
thus, this function on the TCAP will not happen.
11
MC68HC05F8
LOW POWER MODES
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11-1