MC68HC11E0CFNE2 Datasheet, PDF(23/242 Page) Freescale Semiconductor, Inc – M68HC11 CPU, Power-saving stop and wait modes, Low-voltage devices available (3.0–5.5 Vdc)

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MC68HC11E0CFNE2 Datasheet, PDF (23/242 Pages) Freescale Semiconductor, Inc – M68HC11 CPU, Power-saving stop and wait modes, Low-voltage devices available (3.0–5.5 Vdc)

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EXTAL

MCU

XTAL

10 Mâ¦

CL

4xE

CRYSTAL

CL

Pin Descriptions

Figure 1-9. Common Parallel Resonant Crystal Connections

EXTAL

MCU

XTAL NC

4xE

CMOS-COMPATIBLE

EXTERNAL OSCILLATOR

Figure 1-10. External Oscillator Connections

1.4.4 E-Clock Output (E)

E is the output connection for the internally generated E clock. The signal from E is used as a timing

reference. The frequency of the E-clock output is one fourth that of the input frequency at the XTAL and

EXTAL pins. When E-clock output is low, an internal process is taking place. When it is high, data is being

accessed.

All clocks, including the E clock, are halted when the MCU is in stop mode. To reduce RFI emissions, the

E-clock output of most E-series devices can be disabled while operating in single-chip modes.

The E-clock signal is always enabled on the MC68HC811E2.

1.4.5 Interrupt Request (IRQ)

The IRQ input provides a means of applying asynchronous interrupt requests to the MCU. Either negative

edge-sensitive triggering or level-sensitive triggering is program selectable (OPTION register). IRQ is

always configured to level-sensitive triggering at reset. When using IRQ in a level-sensitive wired-OR

configuration, connect an external pullup resistor, typically 4.7 kâ¦, to VDD.

1.4.6 Non-Maskable Interrupt (XIRQ/VPPE)

The XIRQ input provides a means of requesting a non-maskable interrupt after reset initialization. During

reset, the X bit in the condition code register (CCR) is set and any interrupt is masked until MCU software

enables it. Because the XIRQ input is level-sensitive, it can be connected to a multiple-source wired-OR

network with an external pullup resistor to VDD. XIRQ is often used as a power loss detect interrupt.

Whenever XIRQ or IRQ is used with multiple interrupt sources each source must drive the interrupt input

with an open-drain type of driver to avoid contention between outputs.

M68HC11E Family Data Sheet, Rev. 5.1

Freescale Semiconductor

23

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