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 Forum index » DIY Hardware and Software » Arduino
Working the Arduino I/O Ports in BYTE chunks
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State Machine
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PostPosted: Thu Dec 20, 2012 5:57 am    Post subject: Working the Arduino I/O Ports in BYTE chunks Reply with quote  Mark this post and the followings unread

In case you need to work with more than just one PORT bit at a time, here is some good information on I/O PORT manipulation on the Arduino development platform.

http://arduino.cc/en/Reference/PortManipulation

This is also applicable to the read or write of any of the Atmega MCU hardware control registers.

For example, here is a section of code below I needed to write to control TIMER 5 of an Atmega1280 chip on the Arduino MEGA board to output a 2500 Hz, 500 ns pulse on an I/O port bit. You will need to reference the chip data sheet in order to understand what the actual data does:

// timer/counter 5 setup
TCCR5A = B00101001; // Phase and frequency correct PWM change at OCRA
TCCR5B = B00010001; // System clock Select (16 Mhz)
OCR5A = 3200; // Set to 2500 Hz
OCR5C = 4; // Init to .125 % (500 ns PW)

Hope this helps !

Happy Holidays !
Bill
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elmegil



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PostPosted: Thu Dec 20, 2012 6:39 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks!
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State Machine
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PostPosted: Thu Dec 20, 2012 7:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Your very welcome. I have seen this question come up here and there and though it was useful information. I have an example of a FIFO memory read routine I wrote and will post that as another example.

Sure beats reading in PORT bits one by one in a loop and assembling a byte in software (SLOW !!) when you can just read the FIFO a byte at a time and get on with processing the data.

Bill
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cappy2112



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PostPosted: Mon Jan 07, 2013 9:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

State Machine wrote:
Your very welcome. I have seen this question come up here and there and though it was useful information. I have an example of a FIFO memory read routine I wrote and will post that as another example.

Sure beats reading in PORT bits one by one in a loop and assembling a byte in software (SLOW !!) when you can just read the FIFO a byte at a time and get on with processing the data.

Bill


In case it's not obvious to others, the direct port I/O is much faster than digitalWrite(). I had posted some scope screenshots in an Arduino forum on another site, but I forget the actual speed differences.

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PostPosted: Tue Jan 08, 2013 8:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:


The bottom line here is that if digitalWrite() is "real time" enough and you dont care that the bits being manipulated are NOT time aligned, then use it. If speed is a requirment, then use direct port manipulation so long as the bit masking process involved, if required, while operating on single/multiple port bits does not bog your process down.

Bill
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