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M68HC12A4EVB

How to Use the MC68HC812A4 in Special Expanded Narrow Mode Using the M68HC12AEVB

Freescale Semiconductor 

Freescale Semiconductor, Inc.

Engineering Bulletin

Software Setup Using P&E’s SDBUG12 Program

Software Setup Using P&E’s SDBUG12 Program

When using a software debugger in special expanded narrow mode, it is

important to note that the mode register has to be modified.

To start the program, simply get into the directory where the executable

is loaded. Type sdbug12 freq x000000 where x is the A4EVB’s bus

speed.

When this command is typed, either COM1 or COM2 can be used.

Contact P&E Microcomputer Systems, Inc., at its Web site,

www.pemicro.com, for specifics.

Once the SDBUG12 screen is displayed, execute a register modify to

ensure the software is communicating properly with the PC. Type A 55

and watch the screen value for the A accumulator value change. Reset

it to 0 by typing A 00 and observe the A accumulator value change.

So far, the microcontroller is in special single-chip mode. For expanded

narrow mode functionality, the mode register needs to be written twice

with $39 which will provide access to external peripherals in expanded

narrow format and gain access to the bus in 8-bit mode where the data

is provided on data lines d8 to d15.

Make sure the chip select control register (CSCTL) has CSP0 enabled.

Execute a memory modify command by typing mm 3C, and when the

enter key is pressed, the debugger will provide the current value and

designate a field to place the new value in. If the register does not show

the proper value ($20) for CSP0 to be enabled, set it to the proper value.

To check U6B’s accessibility, simply execute a memory modify

command at a memory location inside the RAM’s address space. Type

mm <address>, and the command will respond with the current value

and prompt for the new value.

If this is successful, download an S19 record to the microcontroller,

provided that the record is within RAM’s range.

EB350

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