mc68hc908qf4 Freescale Semiconductor, Inc, mc68hc908qf4 Datasheet - Page 164

• Manufacturer Part Number: mc68hc908qf4
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

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Data Sheet
164
Simple monitor commands can access any memory address. In monitor mode, the
MCU can execute code downloaded into RAM by a host computer while most MCU
pins retain normal operating mode functions. All communication between the host
computer and the MCU is through the PTA0 pin. A level-shifting and multiplexing
interface is required between PTA0 and the host computer. PTA0 is used in a
wired-OR configuration and requires a pullup resistor.
The monitor code has been updated from previous versions of the monitor code to
allow enabling the internal oscillator to generate the internal clock. This addition,
which is enabled when IRQ is held low out of reset, is intended to support serial
communication/programming at 4800 baud in monitor mode by using the internal
oscillator, and the internal oscillator user trim value OSCTRIM (FLASH location
$FFC0, if programmed) to generate the desired internal frequency (1.0 MHz).
Since this feature is enabled only when IRQ is held low out of reset, it cannot be
used when the reset vector is programmed (i.e., the value is not $FFFF) because
entry into monitor mode in this case requires V
remain low during this monitor session in order to maintain communication.
Table 16-1
table, monitor mode may be entered after a power-on reset (POR) and will allow
communication at 9600 baud provided one of the following sets of conditions is
met:
The rising edge of the internal RST signal latches the monitor mode. Once monitor
mode is latched, the values on PTA1 and PTA4 pins can be changed.
Once out of reset, the MCU waits for the host to send eight security bytes (see
16.3.2
consecutive logic 0s) to the host, indicating that it is ready to receive a command.
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•
•
If $FFFE and $FFFF do not contain $FF (programmed state):
–
–
If $FFFE and $FFFF contain $FF (erased state):
–
–
If $FFFE and $FFFF contain $FF (erased state):
–
Freescale Semiconductor, Inc.
Security). After the security bytes, the MCU sends a break signal (10
For More Information On This Product,
The external clock is 9.8304 MHz
IRQ = V
The external clock is 9.8304 MHz
IRQ = V
IRQ = V
shows the pin conditions for entering monitor mode. As specified in the
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TST
DD
SS
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(internal oscillator is selected, no external clock required)
(this can be implemented through the internal IRQ pullup)
TST
on IRQ. The IRQ pin must
MC68HC908QF4 — Rev. 1.0
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