68HC705L16CFU Replacement/Substitute

[kevink]

I need to replace the subject component in a legacy design and am looking for the easiest path to replacement for a part that is currently available.  I would like to port the existing code (if possible).  What would be the best component to replace the functionality of the 68HC705L16 for a current/future design.  I want to minimize the amount of time porting from the legacy device to the new device.

Any suggestions would be appreciated.

[bigmac · Accepted solution]

Hello,

Presumably, the most important aspect of your requirement is the presence of the LCD driver peripheral, and the availability of an 80-pin package to achieve the required number of LCD segments and backplanes.  From the S08 family, a number of MCU types could be investigated to best meet your requirements, e.g. 9S08LG32, 9S08LH64 or 9S08LC60.

All these devices have peripherals that are common to the S08 family, so the recoding requirement would be similar for all.  These devices include many more peripherals than the HC705 device.

I assume that the original code would probably have been assembly code?  Even though the S08 devices will directly handle HC05 instructions, the existing HC05 code will be quite inefficient because direct access to the stack was not available - there are now far more instructions and addressing modes available, including indexed stack.

Regards,

Mac

[kevink]

Thanks for your reply.  My #1 priority is minimizing the code and performance difference between the original implementation and the replacement.  Ideally, I'd like the code to be 100% portable to the new micro, but I recognize this is not a realistic expectation.  I'm not particularly concerned about code efficiency, I want as near to plug and play compatibility as practical.  Does this information help narrow the field of possible replacement options?  I'm looking for a replacement not an improvement or increased capability of the design.

[bigmac]

Hello,

I suggest that you examine the datasheets and/or reference manuals for each of the MCU derivatives previously mentioned, to see which one best suits your needs.

The various peripheral modules that you are using, e.g. timers, LCD driver, SCI, etc., will require to be recoded - they will have different register names, and the operation details will differ from the obsolete product.  Additionally, the memory ranges will also differ.

Another issue will be the assembler that you use.  The CW assembler may not be completely compatible with the previous source code.  If you choose to assemble using the HC05 assembler, you will need to provide the new register names within an include file that is compatible with that assembler, and you will potentially not be able to use CW for programming and debug purposes.  In this event, you may need to purchase a stand-alone programming utility.

Regards,

Mac