MC908QT4MPE datasheet(143/184 Pages) FREESCALE

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Monitor Module (MON)

MC68HC908QY/QT Family Data Sheet, Rev. 5

Freescale Semiconductor

143

If monitor mode was entered with VTST on IRQ, then the COP is disabled as long as VTST is applied to

IRQ.

15.3.1.2 Forced Monitor Mode

If entering monitor mode without high voltage on IRQ, then startup port pin requirements and conditions,

(PTA1/PTA4) are not in effect. This is to reduce circuit requirements when performing in-circuit

programming.

NOTE

If the reset vector is blank and monitor mode is entered, the chip will see an

additional reset cycle after the initial power-on reset (POR). Once the reset

vector has been programmed, the traditional method of applying a voltage,

VTST, to IRQ must be used to enter monitor mode.

If monitor mode was entered as a result of the reset vector being blank, the COP is always disabled

regardless of the state of IRQ.

If the voltage applied to the IRQ is less than VTST, the MCU will come out of reset in user mode. Internal

circuitry monitors the reset vector fetches and will assert an internal reset if it detects that the reset vectors

are erased ($FF). When the MCU comes out of reset, it is forced into monitor mode without requiring high

voltage on the IRQ pin. Once out of reset, the monitor code is initially executing with the internal clock at

its default frequency.

If IRQ is held high, all pins will default to regular input port functions except for PTA0 and PTA5 which will

operate as a serial communication port and OSC1 input respectively (refer to Figure 15-10). That will

allow the clock to be driven from an external source through OSC1 pin.

If IRQ is held low, all pins will default to regular input port function except for PTA0 which will operate as

serial communication port. Refer to Figure 15-11.

Regardless of the state of the IRQ pin, it will not function as a port input pin in monitor mode. Bit 2 of the

Port A data register will always read 0. The BIH and BIL instructions will behave as if the IRQ pin is

enabled, regardless of the settings in the configuration register. See Chapter 5 Configuration Register

(CONFIG).

The COP module is disabled in forced monitor mode. Any reset other than a power-on reset (POR) will

automatically force the MCU to come back to the forced monitor mode.

15.3.1.3 Monitor Vectors

In monitor mode, the MCU uses different vectors for reset, SWI (software interrupt), and break interrupt

than those for user mode. The alternate vectors are in the $FE page instead of the $FF page and allow

code execution from the internal monitor firmware instead of user code.

NOTE

Exiting monitor mode after it has been initiated by having a blank reset

vector requires a power-on reset (POR). Pulling RST (when RST pin

available) low will not exit monitor mode in this situation.

Table 15-2 summarizes the differences between user mode and monitor mode regarding vectors.

MC908QT4MPE Datasheet(PDF) 143 Page - Freescale Semiconductor, Inc

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