PIC18LF4321. What on earth is it?

At the risk of being perceived as a geek, check out this neat microcontroller that I worked on in lab today:

The neat little PIC18LF4321 powered by a 3V coin-cell. Actually strictly speaking, this is a Qwik&Low board which incorporates Microchips’ PIC18LF4321

There you go, don’t be afraid to zoom in.

Low-power designs are the way forward in embedded applications (i’m just lifting off the text, actually written by the prof who’s teaching!), and it’s ability to extend battery life serves countless applications such as heart implants, automobile electronics, ipods, PDAs and many other devices. Pictured above is an 8-bit microcontroller, i.e., it operates on instructions 8 bits at a time. For years, Motorola has dominated the 8-bit microcontroller market. Since 2002, however, the market has been overtaken by Microchip, who passed on reduced costs to consumers, as a result of economies of scale. Therefore, the board used above is a Qwik&Low board that has incorporated Microchips’ PIC18LF4321/2321 package. It has a unit price of about $3.

It is my speculation that these low powered devices make use of diodes which serve as parisitic capacitors that discharge power at low voltages. But these physical features are limited.

That is why it becomes the chip’s perrogative to have several power-saving features. Allow me to briefly explain what some of its features are:

– It has the option of swtiching between INTOSC and INTRC internal oscillators which serve as clocking devices (every computer has a clock, that runs in cycles per unit time known as frequency which is measured in Hertz, e.g. 1 GHz). The INTOSC oscillator draws more power than the INTRC oscillator when the chip is running continuously, and the MSB determines the of the chip’s OSCTUNE register can be set to select high-power but accurate INTOSC or the low-power, less accurate INTRC for less demanding tasks.

– It has a “sleep” mode which is run by a watchdog timer. It has programmable timeout periods of 4ms, 8ms, 16ms, 32ms up to something over 2 mins. Lengthening the period of the timeout can help to reduce average current drawn because the CPU is sleeping during this time. However, it must take into account time intervals to accomodate debouncing of the electromechanical switch.

– Interesting to note is that while using the sleep mode, using a higher frequency INTOSC oscillator actually draws less current than INTRC oscillator ( 5.6 microA vs 49 microA).

– Lastly, the chip has an idle mode, whereby the CPU goes to sleep while performing peripheral tasks, and upon completion awakes the CPU using the chip’s interrupt ciruitry.

I guess that’s about all I can describe about the power-saving features of the chipboard. I have yet to find out what other things it can do! The Qwik&Low board can be linked to a PC via a USB-to-serial adaptor, and it is programmable in C. I may enquire about it’s price and consider getting one of these.

I would say that I kind of enjoyed my lab session today, and it’s so different from what I experience in NTU labs. And I’m thankful for it. The lab assistants don’t press you for time by going through the motions (because lab hours are not limited, it’s OTOT), and I’m not sure about my peers in EEE now, but I wonder if they get to handle such gadgets at all? I got to work on this thing alone, unsupervised, and being able to use the oscilloscope without somebody breathing down your neck was a good respite.

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3 Responses to “PIC18LF4321. What on earth is it?”

  1. Emm Says:

    ive no idea wad u r talking abt. hehe. but i dint exactly read it. hehe. cos its all so technical! =P
    im waiting for u to come over to collect ur sandwich!!! im bored.. thats why im crapping here. hehe. have fun in sch!

  2. Derrick Says:

    Wow, your apartment looks super big man. I’m jealous, I think i lived in a hole when I was in the U.S.. Think the only privilege I had was having the entire room to myself (roomie moved out after a while). Totally dig the lift/elevator conversation…. reminded me of my own ones in Missouri, not that there were lots since the buildings are rarely more than 4 stories high. And I think you write darn well!

    Anyway have fun and study hard too! Get me a CNN T-shirt if you pop by the CNN headquarters ok? (L-Size 🙂 )

    God bless!

  3. Siyi Says:

    Hi Tim

    Looks like you are having fun though I honestly dun know understand what you are talking about (too chim for me), but since you are given the real space to experiment, am expecting some invention from you to be patented in the near future, ha ha…

    Re the lift conversation, sure takes guts and confidence in oneself to do it, over here the reaction is simply in their looks, no words required! But there is hope yet in human nature as elsewhere it seems to work. For starters we have to stop generalising our own people and try doing it here….

    Cheers
    Siyi

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