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Help with RAM selection

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I got to select a micro controller for automotive applications which may go in for production in future. The following functionality to be implemented in the controller RTOS, CAN driver, PWM driver and Diagnostics and other application related software. I have zeroed on microchip with 256K flash and 16k RAM. Now my question is will this 256K flash and 16K RAM will be sufficient or in future memory will not be sufficient. Please help me. Also any other important points i need to keep in mind because once decided and if it is wrong decision it will impact me much.
 

Ian Rogers

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Three chips I've used for the same job..... Pic16f877a 8K Code, 368bytes Ram, 256bytes NV Ram... Had a decent working unit..

Needed to upgrade... Pic18f450.. 32K Code, 1536 bytes Ram, 256 bytes NV Ram...

Needed to upgrade... Pic18f4620.. 64K Code, 3896 bytes Ram, 1K NV Ram...

The point is, the units are pin compatible... If you change the hardware along the line you can change the micro.. If you just need more space, then there will be a bigger chip..

The pic32MX that I'm using has ALL those things you need... The small pic32mx440f256h has 256K Code and 32K of Ram..

There is a pic32mz2048efm64... Same pinout... Brand new... 2M Code and 512K Ram and can run at 200Mhz..

Updating a little later on is simple.... On pic32 dev site there are loads of examples

http://www.microchip.com/wwwproducts/en/pic32mz2048efm064 Then select documentation....
 
Correct but still to avoid rework do you recommend to go for higher memory configuration initially so that it will be some time before i replace the micro. And one more doubt generally what is the external oscillator frequency I have to select that is either 4Mhz or 8Mhz etc.
 

Nigel Goodwin

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Correct but still to avoid rework do you recommend to go for higher memory configuration initially so that it will be some time before i replace the micro. And one more doubt generally what is the external oscillator frequency I have to select that is either 4Mhz or 8Mhz etc.
Ian's point is that there is no 'rework', you simply unplug one PIC and plug in another (that has the same pin connections).

As for clock crystals, it really depends what you need to do - for most application the internal oscillator is fine (as long as the PIC series has that).

I've recently (this week :D) started playing with the PIC24/33/32 series - but mostly the 24. I've bought a MicroStick II which comes with four example PIC's, two 24's, a 33, and a 32. I've also built a further board for my tutorial series, and bought a few 24FJ64GA002 PIC's to play with.

All these PIC's have internal oscillators, avoiding the need for a crystal - unless you need high accuracy, and all are pin interchangeable.

Here's the design of the board, it incorporates a 5V regulator, and a 3.3V regulator (to feed the PIC), the power to the three sockets can be selected with a jumper as either 5V or 3.3V, and there's an LED (connected via another jumper) fed from the same pin as the MicroStickII board - so you can use the demo program that comes with that unit.

PIC24_Top.png PIC24_Bottom.png
 

Ian Rogers

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Correct but still to avoid rework do you recommend to go for higher memory configuration initially so that it will be some time before i replace the micro. And one more doubt generally what is the external oscillator frequency I have to select that is either 4Mhz or 8Mhz etc.
All you do is pick the newest, most available, chip... Some chips that hit the market don't really sell a lot.. You have to pick one that is going to be popular.... These will be the ones selected to be in dev boards... If you go to farnell you can see which are the popular ones..... For you, I recommend the pic32mx795fxxxx... loads of memory and very popular.. ie not going anywhere.... The replacements will be pin compatible...
 
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