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MON12 OPERATION
Mon12 is an embedded monitor / debug utility that allows loading a compiled software program
(S record) into Ram memory for testing and debug. The monitor may control the execution of
the software by applying the SWI software interrupt service. Other features allow memory and
register examination or modification.
Communication with the monitor is provided on the HCS12 SCI0 serial port or COM port on the
development board. Default settings are 9600 baud with 8/n/1 bit settings. Flow control is not
provided so the host PC communication software should be set to None or Hardware flow
control. AxIDE utility software is recommended for use on a windows based host PC.
The monitor relies on resources from the HCS12 target to provide the monitor environment.
The resources include 16K bytes of flash memory and 512 bytes of internal ram memory. The
user must respect the monitor's memory map when applying the monitor to help debug code.
Restricted memory areas:
Monitor Program space: 0xC000 - 0xFFFF Flash or Flash Page $3F.
Monitor Data space:
0x3E00 - 0x3FFF, Internal Ram.
Monitor Console:
COM Port and SCI0.
Monitor Autostart:
0xFEC - 0xFEF, Internal EEprom.
Monitor application provides for redirection of interrupt vectors through the ram based interrupt
table, initialization of SCI0 serial port, initialization of HCS12 flash and EEprom programming
clock rates, initialization of 8 MHz E clock from 4Mhz reference crystal, and detection of auto
start enabled operation. The HCS12 memory map is fixed under monitor operation.
The monitor provides for interrupt vectors in the monitor data space from 0x3F8A - 0x3FFD.
The vectors are in the same order as the default hardware table for the HCS12 located at
address 0xFF8A - 0XFFFD (see table). The Reset vector is reserved, user should apply Auto
Start for application starting from Reset.
MON12 operation notes:
1. CML12S-DP256 monitor application configures target HCS12 for 8MHz E clock, lower flash
block (page $3E) disabled from memory map, and external access clock stretch set to 3
cycles. User can increase clock speed in application by modifying PLL control and setting
new baud rate for serial port. Defaults will return whenever monitor is Reset.
2. Mon12 will not trace into interrupts. To trace an interrupt service set a breakpoint in the
service routine and then trace.
3. Mon12 trace is limited to expecting the next linear address. Program counter modification,
branches, calls, or subroutines will not trace correctly.
4. Monitor start-up procedure:
A) Determine if Auto Start in enabled and proceed to vector if not a value of $FFFF.
