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dluu13
Joined: 28 Sep 2018 Posts: 395 Location: Toronto, ON
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Posted: Wed Oct 31, 2018 10:45 am |
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I checked out the datasheet for some PIC24 units, and that really is a much higher current draw than the PIC16 and 18 units. I'll have to think a bit deeper on my power requirements before I make a decision.
Honestly, I don't require much computation power. It is mostly reading off ADCs and storing them. As for control, it is mostly just controlling a few relays and open loop PWM stuff. The killer for my current setup is the SD card... After seeing temtronic recommend some Vinculum units in another thread, I might consider those instead. I may as well upgrade the MCU though, as a bit of future proofing because I can see myself one day wanting to add more sophisticated controls. |
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asmallri
Joined: 12 Aug 2004 Posts: 1630 Location: Perth, Australia
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Posted: Wed Oct 31, 2018 10:48 am |
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To expand somewhat on Ttelmah's comments
The interrupt table is definitely larger but as program memory on these processors (as a general rule) are significantly larger that the "peer" PIC18F processor, this is not really an issue. In fact the opposite, each peripheral has its own interrupt handler therefore you get to the specific code to deal with that peripheral instead of having to determine the interrupt cause and vector to the appropriate section of the larger interrupt code. In addition the PIC24 optionally support an alternative interrupt vector table (IVT) this enables your application to complete swap the active interrupt vector table. An example use would be a complex bootloader that requires the use of interrupts while the bootloaded application want to the the same interrupts. You can do this by using one IVT for the bootloader and then passing control to the application, swap to the alternate table. There is no such capability with the PIC18.
As a general rule, the PIC24 also has far more RAM that the equivalent pinout sized PIC18 processor.
Regarding the limitation with working with bytes - the native machine size of this processor is 16 bits. Therefore working with 8 bit values does mean dealing with word alignment. This is not a PIC24 issue, this is a processor register size issue and is equally applicable to virtually every non 8 bit processor/ controller/CPU.
The PIC24 is far far more efficient that the PIC18 for any maths operation working on values greater than 8 bits in size. Similarly for pointer manipulation once you need to cross a 256 byte boundary.
As a general rule, the PIC24 does not have an internal data EEPROM however there are PIC24 variants that do and I have used them.
As a general rule, the PIC24 has far more peripherals than the same pinout sized PIC18.
The majority of hardware products I develop today have 16 or 32 bit cores. _________________ Regards, Andrew
http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!! |
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Ttelmah
Joined: 11 Mar 2010 Posts: 19195
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Posted: Wed Oct 31, 2018 11:06 am |
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As one little comment here.
To run the SD card, the best PIC drivers are the ones published by the poster above, Asmallri. Brush Electronics. They do cost a little but are fabulously reliable. He does versions for the PIC18 or the PIC24. With the right SPI drivers they just work.
The PIC18, can handle an SD fine. However preferably a 3.3v chip. A PIC like the PIC18F27K42 works extremely well, and has a lot of peripherals. |
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dluu13
Joined: 28 Sep 2018 Posts: 395 Location: Toronto, ON
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Posted: Wed Oct 31, 2018 11:27 am |
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Ah, looks like it come with the SPI drivers too. That's great! I will keep that in mind as well. |
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jeremiah
Joined: 20 Jul 2010 Posts: 1314
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Posted: Thu Nov 01, 2018 1:25 pm |
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dluu13 wrote: | I checked out the datasheet for some PIC24 units, and that really is a much higher current draw than the PIC16 and 18 units. I'll have to think a bit deeper on my power requirements before I make a decision.
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It depends on the PIC24 parts. If you go PIC24EP of PIC24HJ, they will be higher power. The PIC24F and PIC24FJ series do have many lower power options. We have multiple projects that can average no more than single digit uA's and 100's of nA's using some of the ultra lower power PIC24 options. It's all in the chips you select. Look at the sleep current of the PIC24F32KA304 and similar for example. If you use the chip selector from the microchip website, you can tell it to filter for ultra low power chips. |
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