MC9S12E Motorola, MC9S12E Datasheet - Page 81

• Manufacturer Part Number: MC9S12E
• Description: MC9S12E-Family Device User Guide V01.04
• Manufacturer: Motorola

Freescale Semiconductor, Inc.
Device User Guide — 9S12E128DGV1/D V01.04
2.3.8 PE7 / NOACC / XCLKS — Port E I/O Pin 7
PE7 is a general purpose input or output pin. During MCU expanded modes of operation, the NOACC
signal, when enabled, is used to indicate that the current bus cycle is an unused or “free cycle”. This signal
will assert when the CPU is not using the bus. The XCLKS is an input signal which controls whether a
crystal in combination with the internal Colpitts (low power) oscillator is used or whether Pierce
oscillator/external clock circuitry is used. The state of this pin is latched at the rising edge of RESET. If
the input is a logic low the EXTAL pin is configured for an external clock drive or a Pierce Oscillator. If
the input is a logic high a Colpitts oscillator circuit is configured on EXTAL and XTAL. Since this pin is
an input with a pull-up device during reset, if the pin is left floating, the default configuration is a Colpitts
oscillator circuit on EXTAL and XTAL.
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