Free IO pins

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alexj212
 
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Joined: Wed Jun 04, 2008 9:25 pm

Free IO pins

Post by alexj212 »

This project looks really cool. I was wondering I was reading the specs and I was trying to count unused io pins. Do you know how many pins are available?

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darco
 
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Post by darco »

Here are the pin assignments:

P00 - ENC28J60 RESET
P01 - ENC28J60 CS
P02 - ENC28J60 SCK
P03 - ENC28J60 SI
P04 - ENC28J60 SO
P05 - ENC28J60 WOL
P06 - ENC28J60 INT
P07 - ENC28J60 25MHz Clock

P08 - Speaker
P09 - LED Red
P10 - LED Blue
P11 - LED Green
P12 - TV DAC
P13 - TV DAC
P14 - TV DAC
P15 - 38KHz IR Input

P16 - Button

P28 - Serial EEPROM
P29 - Serial EEPROM
P30 - TX
P31 - RX

So... The total number of unassigned I/O pins is... 11.

However, if you need more I/O, there are a few other options:

The TX/RX pins are for the TTL serial port, which is only used for programming at the moment. Thus you are free to use these if you don't need a serial port.

You could cut the reset trace to the ENC28J60 for P0, as it isn't technically required, allowing you to reclaim another pin. I'd only recommend doing that if you are absolutely needing more I/O.

Since it is a kit, you can feel free to leave out parts like the speaker, the RGB LED, the IR sensor, and the TV DAC depending on what you need or don't need.

I wouldn't recommend leaving out the button if you plan to use the bootloader, as it serves an important function.

P28 and P29 are an I2C bus, so if you have I2C stuff you want to use, you could more than likely share those pins.

So the maximum theoretical number of pins you could have available and still have ethernet connectivity is... 22!

JuJuBee
 
Posts: 18
Joined: Tue Apr 21, 2009 5:32 pm

Re: Free IO pins

Post by JuJuBee »

If I want to hack for VGA - I will need pins 16-23. At this time pin 16 is being used by the reset button. Can I assign a new pin for the reset button, cut the trace for 16, jumber the button to another open pin and then easily find in the bootloader where to change the pin assignment from 16 to another pin? Also, is there TV code for VGA to replace the composite?

This project is great!

Thanks in advance!

JuJuBee

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darco
 
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Joined: Wed Jun 04, 2008 7:54 pm

Re: Free IO pins

Post by darco »

Yes, it would be pretty easy to move the button. If you let me know which pin you plan to move it to I can roll you a custom bootloader for you. P05 would probably be a reasonable choice, considering that it isn't used by anything. Just make sure you cut the trace to the ENC28J60 pin.

If I had this to do all over again I would have not used the ENC28J60 WOL or ENC28J60 RESET pins, which would have freed up two more I/O pins. But oh well. That's life.

JuJuBee
 
Posts: 18
Joined: Tue Apr 21, 2009 5:32 pm

Re: Free IO pins

Post by JuJuBee »

Thanks for your input - then let's choose P05 for the reset button. If at all possible, I would like to keep the composite pins connected as well - what are your thoughts about me using the reset button to toggle between composite and VGA (1024x764) like it currently does with NTSC and PAL? I am not sure about the coding side of things, but would it be an easy change-out in the code for me?

Does the display driver reside in the bootloader along with the TCP/IP stack or within the widget that is loaded afterwords - so I assume the widget also resides in the EEPROM? I could be all fouled up on this....

With the headers - it should give me adequate room for a daughter card - (jus wont fit in the minty enclosure)

The custom bootloader would be greatly appreciated :P

JuJuBee

merchinax
 
Posts: 1
Joined: Sat May 30, 2009 3:24 am

Re: Free IO pins

Post by merchinax »

How can i connect my laptop to my tv if my tv doesnt have a vga input or a dvi input? I bought a vga/hdmi cable and i dont think it would work that way my laptop only has a vga output what can i use
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