mc68hc11d0cfn2 Freescale Semiconductor, Inc, mc68hc11d0cfn2 Datasheet - Page 53

• Manufacturer Part Number: mc68hc11d0cfn2
• Description: M68hc11 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

4.2.4 Clock Monitor Reset
4.2.5 System Configuration Options Register
MC68HC711D3 — Rev. 2
MOTOROLA
The MCU contains a clock monitor circuit that measures the E-clock frequency. If
the E-clock input rate is above approximately 200 kHz, then the clock monitor does
not generate an MCU reset. If the E-clock signal is lost or its frequency falls below
10 kHz, then an MCU reset can be generated, and the RESET pin is driven low to
reset the external system.
The system configuration options register (OPTION) is a special-purpose register
with several time-protected bits. OPTION is used during initialization to configure
internal system options.
Bits 5, 4, 2, 1, and 0 can be written only once during the first 64 E-clock cycles after
reset in normal modes (where the HPRIO register bit (SMOD) is cleared). In special
modes (where SMOD = 1), the bits can be written at any time. Bit 3 can be written
at anytime.
Bits 7, 6, and 2 — Not implemented
IRQE — IRQ Edge/Level Sensitivity Select
DLY — Stop Mode Exit Turnon Delay
CME — Clock Monitor Enable
Address:
Always read 0.
This bit can be written only once during the first 64 E-clock cycles after reset in
normal modes.
This bit is set during reset and can be written only once during the first 64
E-clock cycles after reset in normal modes. If an external clock source rather
than a crystal is used, the stabilization delay can be inhibited because the clock
source is assumed to be stable.
Reset:
Read:
Write:
1 = IRQ is configured to respond only to falling edges.
0 = IRQ is configured for low-level wired-OR operation.
1 = A stabilization delay of 4064 E-clock cycles is imposed before processing
0 = No stabilization delay is imposed after story recovery.
1 = Clock monitor circuit is enabled.
0 = Clock monitor circuit is disabled.
Freescale Semiconductor, Inc.
Figure 4-2. System Configuration Options Register (OPTION)
For More Information On This Product,
resumes after a stop mode wakeup.
$0039
Bit 7
Resets, Interrupts, and Low-Power Modes
0
0
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6
0
0
IRQE
5
0
DLY
4
1
Resets, Interrupts, and Low-Power Modes
CME
3
0
2
0
0
CR1
1
0
Data Sheet
Bit 0
CR0
Resets
0
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