MC68HC908LJ24 Datasheet, PDF(169/464 Page) Motorola, Inc – Microcontrollers

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MC68HC908LJ24 Datasheet, PDF (169/464 Pages) Motorola, Inc – Microcontrollers

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Monitor ROM (MON)

Functional Description

NOTE:

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

an additional reset cycle after the initial POR reset. Once the part has

been programmed, the traditional method of applying a voltage, VTST, to

IRQ must be used to enter monitor mode.

The COP module is disabled in monitor mode based on these

conditions:

â¢ If monitor mode was entered as a result of the reset vector being

blank (above condition set 2 or 3), the COP is always disabled

regardless of the state of IRQ or RST.

â¢ If monitor mode was entered with VTST on IRQ (condition set 1),

then the COP is disabled as long as VTST is applied to either IRQ

or RST.

The second condition states that as long as VTST is maintained on the

IRQ pin after entering monitor mode, or if VTST is applied to RST after

the initial reset to get into monitor mode (when VTST was applied to IRQ),

then the COP will be disabled. In the latter situation, after VTST is applied

to the RST pin, VTST can be removed from the IRQ pin in the interest of

freeing the IRQ for normal functionality in monitor mode.

Figure 10-2 shows a simplified diagram of the monitor mode entry when

the reset vector is blank and just 1 x VDD voltage is applied to the IRQ

pin. An external oscillator of 9.8304 MHz is required for a baud rate of

9600, as the internal bus frequency is automatically set to the external

frequency divided by four.

Enter monitor mode with pin configuration shown in Figure 10-1 by

pulling RST low and then high. The rising edge of RST latches monitor

mode. Once monitor mode is latched, the values on the specified pins

can change.

Once out of reset, the MCU waits for the host to send eight security

bytes. (See 10.5 Security.) After the security bytes, the MCU sends a

break signal (10 consecutive logic 0s) to the host, indicating that it is

ready to receive a command.

MC68HC908LJ24/LK24 â Rev. 2.1

Freescale Semiconductor

Monitor ROM (MON)

Data Sheet

169

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