MC912DG128A Motorola, MC912DG128A Datasheet - Page 34

• Manufacturer Part Number: MC912DG128A
• Description: Microcontrollers
• Manufacturer: Motorola

E-Clock Output
(ECLK)
Reset (RESET)
Pinout and Signal Descriptions
MC68HC912DT128A Rev 2.0
34
XTAL is the crystal output.The XTAL pin must be left without terminal
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 device.
In all cases take extra care in the circuit board layout around the
oscillator pins. Load capacitances in the oscillator circuits include all
stray layout capacitances. Refer to
of oscillator circuits.
ECLK is the output connection for the internal bus clock. It is used to
demultiplex the address and data in expanded modes and is used as a
timing reference. ECLK frequency is equal to 1/2 the crystal frequency
out of reset. The E-clock output is turned off in single chip user mode to
reduce the effects of RFI. It can be turned on if necessary. In special
single-chip mode, the E-clock is turned ON at reset and 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.
An active low bidirectional control signal, RESET, acts as an input to
initialize the MCU to a known start-up state. It also acts as an open-drain
output to indicate that an internal failure has been detected in either the
clock monitor or COP watchdog circuit. The MCU goes into reset
asynchronously and comes out of reset synchronously. This allows the
Pinout and Signal Descriptions
Figure 9 External Oscillator Connections
MCU
EXTAL
XTAL
NC
Figure 8
EXTERNAL OSCILLATOR
CMOS-COMPATIBLE
and
2 x E
Figure 9
for diagrams
MOTOROLA
8-pins