Replacement MCU for MC68340

[ParthRMF]

Hello,  My company is using the MC68340 MCU in a product we manufacture. However it seams that mcu is obsolete now.  What is the closest MCU architecture we could move to that would require minimal firmware changes? Are any of the currently active ColdFire Processers code compactible with MC68340?

Thanks.

[ParthRMF]

Thank you for your help guys.

[Hui_Ma · Accepted solution]

Hi,

Unfortunately, there with no direct (pin to pin compatible) replacement for MC68340 product.
Although some 68K products are not obsolete so far, there with quite few development tools/support resource for those products for a new(replacement) design.

Even ColdFire products are not recommended for new design.

We would recommend customer to use ARM core related MCU products as replacement.
Please refer below links about NXP recommended MCU products, such as i.MX RT products:
Arm®-Based Microcontrollers
i.MX RT Crossover MCUs

Wish it helps.

Mike

[EdwinBland]

A customer of ours has an old product design with a 68340 based MCU in it... which is EOL.  They would like to get another 5years of service on their old design (w/ updates).  They have a replacement product ... but it's not yet complete.

I see Coldfire parts aren't recommended for new designs.  We are trying to see if it makes sense to migrate to a Coldfire based part or simply rip the bandaide off & go to an ARM part.  

Any NXP guidance on the Coldfire availability outlook for the next 5 yrs?

[TomE]

> Any NXP guidance on the Coldfire availability outlook for the next 5 yrs?

NXP guaranteed 10 and 15 year lifetimes, back in 2005 or so:

https://www.nxp.com/products/nxp-product-information/nxp-product-programs/product-longevity:PRDCT_LO...

Given that there's a "replacement product" already in the works, I can't see how starting a different "replacement product" wouldn't slow the first one down.

Replacing the MC68340 with a Coldfire (with the existing other chips) wouldn't be straightforward, as that would most likely require a migration from 5V to 3.3V.

Depending on how much Flash and RAM the existing product uses, you might be able to use a Coldfire chip with enough internal Flash and RAM, simplifying the product. But the same goes for using an ARM based chip. The main problem you might have with ARM depends on how much the existing code has big-endian dependencies.

I'd recommend against using an i.MXRT if you can use a simpler chip. There's a lot less work getting the peripherals working as the i.MXRT ones are very powerful, but also very complicated. Something closer to the MC68340 modules would make porting the existing code easier.

Tom

[TomE]

Availability? Just type "Longevity" into NXP's site and you'll get a very good web page on just that:

https://www.nxp.com/products/nxp-product-information/nxp-product-programs/product-longevity:PRDCT_LO...

Filter on "32-bit Coldfire" and you'll see that they range from 2005 to 2010 with "10 year longevity" and ones from 2007 to 2010 with "15 year longevity". That said, we're still buying the MCF5235, which is a "2005 10 year" part. It looks like NXP will keep making popular parts that there's enough of a demand for.

"EOL", but possibly still available (except for the chip shortages). Don't ignore the sense of a "Last Time Buy" to get enough for that 5 year requirement. Maybe that should have been done a few years ago.

It seems to me that spending time on a "quick-fix substitute" might take resources away from "the replacement product". It might even take longer to get this one working than getting the existing replacement working. Unless the "Replacement" has fallen victim to the "Second System Effect".

There's no "drop in replacement" for the MC68340. Were you using the MC68340 or the MC60340V? The reason I ask is that AFAIK all the Coldfire parts are 3.3V. If the existing board isn't using the "V" (3.3V) part, then you won't be able to put a 3.3V ColdFire (or ARM) chip on the board with existing 5V parts. Everything else has to be replaced to get to 3.3V as well. Or you need "level shifters", and that's a pain.

The MC68340 has no internal RAM or FLASH, so it must be using external. How much? A little or a lot? Can you replace the CPU and RAM and FLASH with a Microcontroller with enough internal memory so you don't need any external? That would help to simplify the design.

There's another problem with starting a ColdFire design now. You can't get development boards any more. It is always better to start on a supported development board (with supplied code that runs on it), but you had to do that 12-19 years ago. If you just drop an unfamiliar CPU onto an existing board, debugging that can easily take a very long time.

You could emulate the 68k on a faster CPU if necessary. The MC68340 only ran at 25MHz maximum on a 16 bit external bus with a 2 clock minimum instruction execution time.

You could probably get away with a 5V PIC!

How "bad" is the existing software? How much is in assembly? How much directly accesses the hardware devices (instead of being abstracted via generic device drivers)? How much code is written assuming and relying on the big-endian byte order? So how much effort would there be in rewriting the existing code?

What about future support of the product? Does it need field software updates? Does it need to be repaired over the next 10 years? Can you get the spare parts to repair them?

There's no simple answers here. This is a "Real Engineering Project".

Tom

[TomE]

This App Note details how to transition to a Coldfire chip from an MC68340:

https://www.nxp.com/docs/en/application-note/AN2007.pdf

But you should have done that 22 years ago, and the Coldfire chip that suggests is EOL.

What features of the MC68340 are you using? Are you using the DMA? The Timers? Do you have hardware that depends critically on the bus timing? Does the software depend on the big-endian CPU architecture? Those are the things that constrain your choices.

The firmware is going to have to change, so you might as well fix more of that to get to a modern CPU platform.

Tom

All Coldfire chips are "too old" for a new design.