Monitor ROM (MON)
Table 10-3 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 Section 23. Electrical
Specifications for this limit.
Table 10-3. Monitor Baud Rate Selection
External
Frequency
Internal
Frequency
Baud Rate
(BPS)
IRQ
PTC1
V
4.9152 MHz
9.8304 MHz
9.8304 MHz
32.768 kHz
0
1
2.4576 MHz
2.4576 MHz
2.4576 MHz
2.4576 MHz
9600
9600
9600
9600
TST
TST
V
V
X
X
DD
V
SS
10.4.5 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)
The monitor ROM firmware echoes each received byte back to the PTA0
pin for error checking. An 11-bit delay at the end of each command
allows the host to send a break character to cancel the command. A
delay of two bit times occurs before each echo and before READ,
IREAD, or READSP data is returned. The data returned by a read
command appears after the echo of the last byte of the command.
NOTE: Wait one bit time after each echo before sending the next byte.
Technical Data
164
MC68HC908LJ12 — Rev. 2.1
Freescale Semiconductor
Monitor ROM (MON)
FREESCALE [ Freescale ]
