Introducing Buffalo: The Config. Register

The 68HC11E9 chip comes with a sizable ROM in the upper part of the memory map. The 68HC11E9BCFN2 in particular uses that on-chip ROM to store the BUFFALO monitor. If the ROM is disabled, you might need to re-enable it somehow. The CONFIG register has the master controls for enabling the Buffalo ROM, EEPROM, and the COP timer. The CONFIG register is implemented with EEPROM memory and retains its settings. A write to the CONFIG register is only seen following reset.

While the AXIOM tools, the program JBUG11, and Buffalo each provide a mechanism for changing the value in the CONFIG register, the following is a simple manual method for re-enabling on-chip ROM. Do the following:

Set the mode to bootstrap by making MODA and MODB low, apply power, and assert RESET a few times. Turn off the power.
Change to single-chip mode by leaving MODA low and making MODB high and check that pin E0 is not high, your board should have a pull-down resistor on pin E0 already. Next, apply power. Without external memory, the need for on-chip memory over-rides the configuration register, hence Buffalo starts for you.
In Buffalo, use the MM command to change the CONFIG register value, the value $0F in the 68HC11E9 turns off the COP, enables on-chip ROM, and enables on-chip EEPROM.
```
>mm 103f

103F 0D 0F

rom-
>
```
The CONFIG register is only updated, following a reset, so press reset once more.

Now you can set the CPU mode and pick up where you left off. If you are using the Axiom CME11E9, switch to expanded mode by making MODA and MODB both high. If you are using a U.H. educational board, leave the board in single chip mode.

Copyright Notice

This tutorial page was written for EE332, the Introduction to Microprocessors course offered by the Electrical Engineering Department in the College of Engineering at the University of Hartford. Copyright is dated October 18, 2001 and is reserved by the author, Jonathan Hill. Permission is granted to make copies of this document for educational use as-is, provided that this statement remains attached. I do strive to improve this document, please forward constructive criticism and suggestions. Credits will be added as improvements are made.
Original Author: Jonathan Hill (jmhill@mail.hartford.edu)
Last Modified: Fri Dec 13 17:05:34 EST 2002

jmhill@hartford.edu