Motorola MC9S12GC-Family warranty Bkgd / Taghi / Modc Background Debug, Tag High & Mode Pin

Device User Guide — 9S12C128DGV1/D V01.05

2.3.5 BKGD / TAGHI / MODC — Background Debug, Tag High & Mode Pin

The BKGD / TAGHI / MODC pin is used as a pseudo-open-drain pin for the background debug communication. In MCU expanded modes of operation when instruction tagging is on, an input low on this pin during the falling edge of E-clock tags the high half of the instruction word being read into the instruction queue. It is also used as a MCU operating mode select pin at the rising edge during reset, when the state of this pin is latched to the MODC bit.

2.3.6 PA[7:0] / ADDR[15:8] / DATA[15:8] — Port A I/O Pins

PA7-PA0 are general purpose input or output pins,. In MCU expanded modes of operation, these pins are used for the multiplexed external address and data bus. PA[7:1] pins are not available in the 48 package version. PA[7:3] are not available in the 52 pin package version.

2.3.7 PB[7:0] / ADDR[7:0] / DATA[7:0] — Port B I/O Pins

PB7-PB0 are general purpose input or output pins. In MCU expanded modes of operation, these pins are used for the multiplexed external address and data bus. PB[7:5] and PB[3:0] pins are not available in the 48 nor 52 pin package version.

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 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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