Configuration and Setup
Using Fast External RAM
M68HC12A4EVB Evaluation Board — Rev. 1
User’s Manual
MOTOROLA
Configuration and Setup
33
2.7.2 Reprogramming the RAM Chip Select
Either of two methods may be used to reprogram the RAM chip select, CSD, to
eliminate the wait state.
NOTE:
Before attempting either of the following methods, ensure that the EVB is
operating properly by following the startup instructions in
3.2 Startup
.
Method A — Modifying the CSSTR0 register in memory (temporary)
This method may be used without altering the D-Bug12 startup code in
EPROM. However, it must be repeated each time the EVB is powered up or
reset.
Using D-Bug12’s MM (MEMORY MODIFY) command, change the value at
memory location $003E from $05 to $04.
Method B — Modifying the D-Bug12 startup code in EPROM (permanent)
This method is accomplished by reprogramming a single byte in the
factory-supplied, one-time-programmable (OTP) EPROM, U7. An EPROM
programmer is required.
NOTE:
Method B does not work in reverse. If U7 has already been reprogrammed
using this technique, it cannot be restored to its original state.
If the EPROMs are to be customized in some other way — for example, to add
a user program or to modify another aspect of D-Bug12 — the change to
register CSSTR0 can be made in the startup source code. For more information,
refer to
Appendix C. D-Bug12 Startup Code
and
Appendix E. Customizing
the EPROMs
.
To permanently reprogram U7 for zero RAM wait states, follow these steps:
1.
Remove power from the EVB.
2.
Being careful not to bend any pins, remove U7 from its socket on the
EVB and install it in the appropriate socket on the EPROM programmer.
3.
Following the instructions and using the software for the EPROM
programmer, perform the steps in procedure 1 or procedure 2, as
described here.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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