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Speed on 18F4620

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3v0

Coop Build Coordinator
Forum Supporter
Ok guys. Exact timing shouldnt be a issue for my project. I need help with speed.

Should i use a 20mhz crystal or 8mhz int with PLL ?

You did not give us much to go on. The internal with PPL will clock at 32MHz as opposed to the more precise 20MHz crystal. Without reading you mind regarding the application I suggest you go with 32MHz in that you have more processiong power and save the cost of the crystal.

3v0
 
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AtomSoft

Well-Known Member
Hey yeah sorry it's for my LCD stuff I fin the drawing to be slow. I would like to speed it up. I was reading the datasheet and noticed a 10mhz crystal with HSPLL would give me 40mhz aka 10mips which should be decent.
 

3v0

Coop Build Coordinator
Forum Supporter
This is a bit disjointed as I am running out of time and also helping on chat.

Hey since u have been around pics longer and obviously know more which pic can u recommend to top the 18f4620 in speed and ram?

Some of the 18F family go up to 16 MIPS which is 6 Mips faster then the 18F4620. A good example is the PIC18F43K20. But there is a problem.

The problem is that it is not supported by PICkit2 for program or debug. It is supported by ICD2 so if you have a inchworm and the companion board that converts it to USB you are in buisness.

I am guessing it is a speed issue with the PICkit2 and none of the chip over 40 Mhz (10 MIPs) will work with it. Not 100% sure.

You could move up to 24s and dsPICs but I do not think that is what you are looking to do.

Also you need to check the datasheet on the 4620.
"The HSPLL mode makes use of the HS Oscillator
mode for frequencies up to 10 MHz. A PLL then multiplies
the oscillator output frequency by 4 to produce an
internal clock frequency up to 40 MHz."

In short you can not use a 20MHz crystal and the PLL. You need to use a 10MHz and the PLL for 40MHz aka 10Mips..

3v0
 
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AtomSoft

Well-Known Member
yeah i knew that about the 10mhz to 40 mhz to make 10 mips thing .... i guess ill look into 16bit and 32bit PIC Micros mainly because its about time i upgraded since i will be trying to do some imaging and video on these things heh and will be working with a large amount of data.. I might as well go bigger... I do have a ARM7 dev board but i feel like its not worth my time to switch over heh but i might just do ARM7 since they are so powerfull and have nice storage.

Also (i use C) so i can port a lot if not all over to it.
 
18f4620 Overclocking

We overclock our 18f4620s.

We use a 12 Megaherz crystal with the internal x4 giving us 48 Mhz. Works great - been doing this for years - but don't go over that. We were doing around 56 for a while during early development and that was too high.

We use 18f4620s in our network hardware and need the speed.

Mark Woodford
Networked Robotics Corporation
 
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