MC68HC912BL16 Datasheet, PDF (11/128 Pages) Freescale Semiconductor, Inc – 16-Bit Microcontroller

Freescale Semiconductor, Inc.
EXTAL
MCU
XTAL
10 MΩ
C
2xE
CRYSTAL
C
Figure 4 Common Crystal Connections
COMMON XTAL CONN
EXTAL
MCU
XTAL _NC
2xE
CMOS-COMPATIBLE
EXTERNAL OSCILLATOR
Figure 5 External Oscillator Connections
EXT EXTAL CONN
XTAL is the crystal output. The XTAL pin must be left unterminated when an external CMOS compatible
clock input is connected to the EXTAL pin. The XTAL output is normally intended to drive only a crystal.
The XTAL output can be buffered with a high-impedance buffer to drive the EXTAL input of another de-
vice.
In all cases take extra care in the circuit board layout around the oscillator pins. Load capacitances
shown in the oscillator circuits include all stray layout capacitances. Refer to Figure 4 and Figure 5 for
diagrams of oscillator circuits.
3.3.2 E-Clock Output (ECLK)
ECLK is the output connection for the internal bus clock and is used to demultiplex the address and data
and is used as a timing reference. ECLK frequency is equal to 1/2 the crystal frequency out of reset.
In normal single-chip mode the E-clock output is off at reset to reduce the effects of RFI but can be
turned on if necessary.
In special single-chip mode the E-clock output is on at reset but can be turned off.
In special peripheral mode the E clock is an input to the MCU.
All clocks, including the E-clock, are halted when the MCU is in STOP mode. It is possible to configure
the MCU to interface to slow external memory. ECLK can be stretched for such accesses.
MC68HC912BL16TS/D
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