hi,
In arduino i like to change the external cystal ocsillator ( 16 Mhz) to internal RC oscillator of 8 Mhz.
Is there any way to change
plz reply me
Thanks
hello friends
Anyone plz clear my doubt.
In arduino i like to change the external cystal ocsillator ( 16 Mhz) to internal RC oscillator of 8 Mhz.
Is there any way to change
plz reply me
Thanks
Why do you want to do that? There are a lot of things that depend on the crystal frequency. Changing all of them is not trivial.
to internal RC oscillator of 8 Mhz.
The internal oscillator is about 1MHz. Once you change to it you won't be able to use serial to down load your code as the baud rates will be screwed up.
To change it you need to change a bit in the fuse settings. See the data sheet for the ATmeg processor you have. You can only do this with a programmer of some description.
Do you still want to do it? If so why?
See this thread:-
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1163418637
This is not something you can do from within the Arduino development environment. Changing clock source requires the use of an external programmer and altering a fuse setting.
To get started on how - you can try google with keywords "arduino programmer fuse".
The AtMega's (168/328) have an internal 8MHz oscillator and this is a good alternative for custom designs. Also boards like the "Mini Pro 3V3" run at 8MHz and they work well with the Arduino core and with the "official" libraries.
The data sheet says:-
The device is shipped with internal RC oscillator at 8.0MHz and with the fuse CKDIV8 programmed,
resulting in 1.0MHz system clock. The startup time is set to maximum and time-out
period enabled. (CKSEL = "0010", SUT = "10", CKDIV8 = "0"). The default setting ensures that
all users can make their desired clock source setting using any available programming interface
1 MHz is the speed they run at fresh from the factory. Setting CKDIV8=1 (that is to switch it off) will change this to 8MHz. The internal osscilator can also be calibrated through a CPU register (OSCCAL) and as such can be made highly accurate and suitable also for clock sensitive applications.
If speed is less of an issue (as is the case for a broad range of applications) being able to just drop the external crystal/oscillator simplifies the design and reduces cost.
As for reprogramming existing hardware already operating with a crystal, I can't really see the point. I assume however the original poster had something else in mind.
onYa BenF
The internal osscilator can also be calibrated through a CPU register (OSCCAL) and as such can be made highly accurate and suitable also for clock sensitive applications.
It depends on what you mean by highly accurate. According to the datasheet, the internal oscillator calibration accuracy can be improved from plus/minus 10% to plus/minus 1%. A clock running with 1% accuracy could have an error of almost 90 seconds per day. Arduino running from a crystal is accurate to a few seconds per day.
Thankyou all for ur replies
Actually i want to use the multiplexed pins ( 9 & 10 of Atmega8)
as general purpose ports ( PB6 & PB7), instead of using external crystal there. Thatwhy i thought ofconfiguring internal RC ocsillator , so as to make that two pins free.
Plz reply me any options there to make my 9th and 10th pin free from using as external crystal
Thankyou all
Plz reply me any options there to make my 9th and 10th pin free from using as external crystal
There is an article here that describes how to do it: Wolf Paulus' Journal
But it's a lot of work to get 2 more pins. If you are not comfortable with fuse settings and changing bootloaders you may want to consider a board with a chip having more IO pins, like one of these:
Sanguino: http://sanguino.cc/
Gator : http://www.ruggedcircuits.com/html/mb324p_nc.html
Teensyduino: Teensyduino - Add-on for Arduino IDE to use Teensy USB development board
The last one is very cool, its tiny, with onboard USB and has 3 full 8 bit ports available.