Which device can I use to replace a MC68HC705B16CFN ?

[patrickdurham]

I have using this chip (MC68HC705B16CFN) for well over 10 years.  I'm having a lot of trouble finding these chips.  I'd like to update to a newer chip that can accept the program file that is being used for the MC68HC705B16CFN.  It's been many years since I have had to deal with programming, so I would not like to start over with the programming.  I've looked around to try to find a suitable replacement, but have come up short.  My application uses the A/D input on PD3.  I believe this is why I've been coming up short.  Is there any hope for me to find such a replacement?

[david_diaz]

Hello Patrick,

Indeed, all the HC05 family of parts are in the phase out mode. They are legacy parts.

Unfortunately we do not have a direct replacement for the MC68HC705B16CFN device, but a good recommendation would be the S08 family, however, that does not make it pin to pin compatible.

A suggested replacement would be the S08AW 8-bit MCU family.

S08AW 8-bit Microcontroller Family web page: Overview, Documentation, Software & Tools, Orderable parts:

8-bit General Purpose AW60/48/32/16 MCUs|Freescale

The S08AW family belongs to the Product Longevity Program. That means that Freescale makes a broad range of devices available for a minimum period of 10 and 15 years.

Please find more information about the Product Longevity Program at:

Product Longevity - Archived|Freescale

Please refer to the following information that could be useful for you in case you decide to move to the S08 family:

Application Note AN1218

Application Note AN2717

In case you need a specific recommendation, please let me know the necessities of your project.

Hope this information will be useful for you.

Have a great day :smileyhappy:

Best Regards,

David Diaz

[tonyp]

It seems you're looking for a pin-to-pin replacement, or close enough.

My thoughts:

Using another HC05 is obviously pointless.

The only reasonable alternative to keep changes to a minimum is to move to a S08.  Although an S08 is source code and object code backwards compatible to the HC05, that's where the similarity ends.

Memory layout, or accessing MCU peripherals (like the A/D) is not 100% compatible, so some code rewriting will most likely be required.  So, if you only have the binary image of the app, it won't be easy, as you would first have to disassemble the code.

Solving pin-out issues is a smaller problem as you should be able to make an add-on mini PCB to convert another MCU's pin-out to your original.

I don't think you would have to write your code from scratch.  It's fairly easy and straight forward to convert HC05 code to S08, and to also take advantage of the new capabilities.  However, you would need to have the source code.  Do you have it?  In what language?

(BTW, I may be able to help with the conversion as I've done this many-many times already.)

[patrickdurham]

Hello Sir,

Are all HC05 chips out of production? Why would

another HC05 be pointless?

Thank you,

Patrick Durham

VP of Operations

Machine Control Systems, Inc.

<patrick@machinecontrolsystemsinc.com>

[tonyp]

They are all not recommended for new designs.

From Freescale's web site the only member with enough memory to be memory-size compatible with the B16 is the C9A.

68HC705C9A|8-bit Microcontroller (MCU)|Freescale

If you follow the Buy link:

68HC705C9A|8-bit Microcontroller (MCU)|Freescale

you'll see that it is End of Life and no longer manufactured.

So, HC05 replacement is pretty much out the of question unless you can find some source that has new old stock that can cover you.

[patrickdurham]

Hello Sir,

So, where do I go from here? Can you suggest an S08 part number?

And what about the A/D converter?

Thank you,

Patrick Durham

VP of Operations

Machine Control Systems, Inc.

<patrick@machinecontrolsystemsinc.com>

[tonyp]

That depends on a lot of factors: How many I/O pins you need, RAM & ROM sizes, etc.

There are a lot of options in the S08 range.  I think the only one available that would work with the minimum changes for you is the FL16 as it has the same memory, it's DIP and 5V so it covers basic compatibility, and its status is 'active'.

8-bit Cost-Effective FL16/8 MCUs|Freescale

Specifically the MC9S08FL16CBM