MC68HC08XL36 Datasheet, PDF (155/362 Pages) Freescale Semiconductor, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Monitor ROM (MON)
Functional Description
The PLL can be engaged to increase the baud rate of instruction transfer
between the host and the MCU and to increase the speed of program
execution. Monitor mode must be entered with PTC high to use the PLL.
See Entering Monitor Mode on page 152. Initially, the bus frequency is
a divide-by-four of the input clock.
After the PLL is programmed and selected as the base clock,
communication between the host and MCU must be re-established at
the new baud rate. One way to accomplish this is with a program
downloaded from the host into the MCU RAM. The downloaded routine
can program the PLL and send a new baud rate flag to the host just
before engaging the PLL onto the bus. Then an SWI instruction can be
used to return program control to the monitor firmware.
Commands
The monitor ROM firmware uses the following commands:
• READ (read memory)
• WRITE (write memory)
• IREAD (indexed read)
• IWRITE (indexed write)
• READSP (read stack pointer + 1)
• RUN (run user program)
The monitor ROM firmware echoes each received byte back to the PA0
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.
7-mon08sp_1p
MOTOROLA
Monitor ROM (MON)
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MC68HC08XL36
155