18LF devices and internal oscillator

[edeca]

Quick and probably silly question.. do the LF devices have different internal oscillators?

The only difference I can see in the datasheet is when using A/D features, the maximum device speed is about half.

It normally wouldn't matter but I managed to order the wrong samples and I really want to get my LCD working so I need the delay loops to work correctly

 

[joshua17ss2]

The LF in the chip usually means that there is a different voltage range when compared to the 18F series, I believe the 18LF series has a lower operating voltage. Most compilers will come with an include file for the LF series of chips.
hope this helps
josh

 

[edeca]

Yep, obviously the 18LF devices can tolerate a much lower operating voltage. The 18LF1320 also works at 5v though and programs fine with a 5v Junebug

However, I was wondering whether the internal oscillator was any different to help with lower power requirements. The only thing that made me wonder was the notes in the A/D section of the datasheet, nothing else seems to indicate anything special.

 

[Mike - K8LH]

Doesn't the operating voltage affect the maximum clock frequency you can use on some devices? I seem to recall one chap who couldn't use the INTOSC at 8 MHz on his PIC when he was running at 3 volts or 2.6 volts or something like that.

 

[edeca]

Doesn't the operating voltage affect the maximum clock frequency you can use on some devices? I seem to recall one chap who couldn't use the INTOSC at 8 MHz on his PIC when he was running at 3 volts or 2.6 volts or something like that.

That's what I'm not sure about, I think I remember reading similar. I plan on running mine at 5v until I get a non-LF part!

 

[futz]

The only difference I can see in the datasheet is when using A/D features, the maximum device speed is about half.

What page? I did a bit of skimming thru it and couldn't find anything like that.

There's no separate datasheet for the LF part, is there? I'm looking at the 18F1220/1320 datasheet. Couldn't find a LF sheet.

 

[Mike - K8LH]

Figure 22-3 in the Data Sheet shows maximum clock frequency to voltage. Max' is 4 MHz with Vdd = 2.0 volts for the 'LF1230/1330.

 

[futz]

Figure 22-3 in the Data Sheet shows maximum clock frequency to voltage. Max' is 4 MHz with Vdd = 2.0 volts for the 'LF1230/1330.

Ya, I knew that, but that has nothing to do with A/D.

 

[edeca]

Ya, I knew that, but that has nothing to do with A/D.

Page 161. One of the only references I can find to a difference between LF and normal devices apart from the voltage range. Perhaps I'm misinterpreting it, it's not important for me at the moment anyway.

Thanks for the pointer to image 22-2 Mike, that's excellent. I'm running at 5v so my question is now answered.

With 1001 things to learn (cycles per instruction for delays, how to define variables using cblock etc.) it's slow progress, but I think I'll have a working LCD before the end of the world. Thanks again to futz for the example code on your website, I've been picking up more hints from there

 

[Mike - K8LH]

edeca, what development language are you using on your projects?

 

[edeca]

edeca, what development language are you using on your projects?

Learning the very basics using ASM then hopefully moving onto one of the C compilers later. Oddly enough the assembly isn't too hard because I know a bit of x86, it's more learning the hardware.

I know there are cut-and-paste examples for everything already but I'm trying to learn more by doing things the hard way. And probably asking more stupid questions too

Why do you ask?

 

[Mike - K8LH]

I was just curious.

Enjoy the journey. Have fun. Mike

 

[futz]

Page 161. One of the only references I can find to a difference between LF and normal devices apart from the voltage range. Perhaps I'm misinterpreting it, it's not important for me at the moment anyway.

Ah, I see. All that says is that if you're running in a low power mode (power saving) you should adjust your A/D settings to suit, and don't change clock speed while converting. Nothing about having to run at half speed.

The only thing you have to worry about is the same old thing. If you're running with reduced power (less than 5V) you have to reduce clock speed accordingly.

Another thing to think about - if you're running at less than 3V and wanting 10-bit results out of the A/D, you're not going to get it. These things require minimum 3V to get 10-bit accuracy. So in that case you'd have to run an external voltage reference.