MC908GR8CDWE Datasheet, PDF (197/408 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Freescale Semiconductor, Inc.
Monitor ROM (MON)
Functional Description
15.4.4 Baud Rate
The communication baud rate is controlled by the crystal frequency upon
entry into monitor mode. The divide by ratio is 1024.
If monitor mode was entered with V_DD on IRQ, then the divide by ratio is
also set at 1024. If monitor mode was entered with V_SS on IRQ, then the
internal PLL steps up the external frequency, presumed to be 32.768
kHz, to 2.4576 MHz. These latter two conditions for monitor mode entry
require that the reset vector is blank.
Table 15-3 lists external frequencies required to achieve a standard
baud rate of 9600 BPS. Other standard baud rates can be accomplished
using proportionally higher or lower frequency generators. If using a
crystal as the clock source, be aware of the upper frequency limit that the
internal clock module can handle. See 5.0 V Control Timing and 3.0 V
Control Timing for this limit.
Table 15-3. Monitor Baud Rate Selection
External
Frequency
9.8304 MHz
9.8304 MHz
32.768 kHz
IRQ
V_TST
V_DD
V_SS
Internal
Frequency
2.4576 MHz
2.4576 MHz
2.4576 MHz
Baud Rate
(BPS)
9600
9600
9600
15.4.5 Commands
The monitor ROM firmware uses these commands:
• READ (read memory)
• WRITE (write memory)
• IREAD (indexed read)
• IWRITE (indexed write)
• READSP (read stack pointer)
• RUN (run user program)
MC68HC908GR8 — Rev 4.0
MOTOROLA
Monitor ROM (MON)
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Technical Data
197