Datasheet

Chapter 5 Resets, Interrupts, and System Configuration
MC9S08JM60 Series Data Sheet, Rev. 3
Freescale Semiconductor 73
5.7.2 System Reset Status Register (SRS)
This register includes seven read-only status flags to indicate the source of the most recent reset. When a
debug host forces reset by writing 1 to BDFR in the SBDFR register, none of the status bits in SRS will
be set. Writing any value except 0x55 and 0xAA in sequence to this register address causes the MCU reset
with the source of COP. The reset state of these bits depends on what caused the MCU to reset.
2
IRQACK
IRQ Acknowledge — This write-only bit is used to acknowledge interrupt request events (write 1 to clear IRQF).
Writing 0 has no meaning or effect. Reads always return 0. If edge-and-level detection is selected (IRQMOD = 1),
IRQF cannot be cleared while the IRQ pin remains at its asserted level.
1
IRQIE
IRQ Interrupt Enable — This read/write control bit determines whether IRQ events generate an interrupt
request.
0 Interrupt request when IRQF set is disabled (use polling).
1 Interrupt requested whenever IRQF = 1.
0
IRQMOD
IRQ Detection Mode — This read/write control bit selects either edge-only detection or edge-and-level
detection. See Section 5.5.2.2, “Edge and Level Sensitivity,” for more details.
0 IRQ event on falling/rising edges only.
1 IRQ event on falling/rising edges and low/high levels.
76543210
R POR PIN COP ILOP 0 LOC LVD —
W Writing any value to SRS address clears COP watchdog timer.
POR10000010
LVR:U0000010
Any other
reset:
0
(1) (1) (1)
0
(1)
00
U = Unaffected by reset
1
Any of these reset sources that are active at the time of reset will cause the corresponding bit(s) to be set; bits corresponding
to sources that are not active at the time of reset will be cleared.
Figure 5-3. System Reset Status (SRS)
Table 5-3. SRS Register Field Descriptions
Field Description
7
POR
Power-On Reset — Reset was caused by the power-on detection logic. Because the internal supply voltage was
ramping up at the time, the low-voltage reset (LVR) status bit is also set to indicate that the reset occurred while
the internal supply was below the LVR threshold.
0 Reset not caused by POR.
1 POR caused reset.
6
PIN
External Reset Pin — Reset was caused by an active-low level on the external reset pin.
0 Reset not caused by external reset pin.
1 Reset came from external reset pin.
Table 5-2. IRQSC Register Field Descriptions (continued)
Field Description