Datasheet

Monitor ROM (MON)
Functional Description
MC68HC908JB8•MC68HC08JB8•MC68HC08JT8 — Rev. 2.3 Technical Data
Freescale Semiconductor Monitor ROM (MON) 169
Table 10-2 is a summary of the vector differences between user mode
and monitor mode.
When the host computer has completed downloading code into the MCU
RAM, the host then sends a RUN command, which executes an RTI,
which sends control to the address on the stack pointer.
10.4.2 Baud Rate
The communication baud rate is dependant on oscillator frequency,
f
XCLK
. The state of PTA3 also affects baud rate if entry to monitor mode
is by IRQ =V
DD
+V
HI
. When PTA3 is high, the divide by ratio is 625. If
the PTA3 pin is at logic zero upon entry into monitor mode, the divide by
ratio is 312.
Table 10-2. Monitor Mode Vector Differences
Modes
Functions
COP
Reset
Vector
High
Reset
Vector
Low
Break
Vector
High
Break
Vector
Low
SWI
Vector
High
SWI
Vector
Low
User Enabled $FFFE $FFFF $FFFC $FFFD $FFFC $FFFD
Monitor
Disabled
(1)
$FEFE $FEFF $FEFC $FEFD $FEFC $FEFD
Notes:
1. If the high voltage (V
DD
+ V
HI
) is removed from the IRQ pin or the RST pin, the SIM
asserts its COP enable output. The COP is a mask option enabled or disabled by the
COPD bit in the configuration register.
Table 10-3. Monitor Baud Rate Selection
Monitor Mode
Entry By:
Oscillator Clock
Frequency, f
CLK
PTA3 Baud Rate
IRQ
= V
DD
+ V
HI
3 MHz 0 9600 bps
6 MHz 1 9600 bps
3 MHz 1 4800 bps
Blank reset vector,
IRQ
= V
DD
6 MHz X 9600 bps
3 MHz X 4800 bps