using raspberry pi ports

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deadshot
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using raspberry pi ports

Postby deadshot » Thu Dec 19, 2013 4:29 pm

Quick question on the new startKit broad. The hardware manual states “LEDs are not available if the J3 (Raspberry Pi) header is in use” How does this work…what disconnects the LEDs. I ask this because I am looking to use the XOD56 through XOD70 ports for something else (VGA output) and I do not want the LEDs to interfere with my output on those ports.
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infiniteimprobability
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Postby infiniteimprobability » Thu Dec 19, 2013 6:04 pm

Most of the RPI port is P32A (which can only all input or all output) and uses the same lines connect to LEDs. So there's no fundamental reason why you can't output values to both the pin and the LED (subject to how much you want to drive).
Using LEDs at the same time as having an RPI connected is not ideal though - unless you ensure the RPI I/O doesn't care about this. This is because you'll be driving PWM into quite a few of the lines..
At statup, the pulsating X demo drives many of the LEDs, so in this case, it's best to load an empty program

Code: Select all

main{return 0;}
will do it.. into flash to stop it booting the default OTP demo.
deadshot
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Postby deadshot » Fri Dec 20, 2013 4:39 am

So if I want to create a VGA driver and use the p32a port as the output (5x5x5 rgb)...the LEDs will still be driven by the driver. There is no way to disconnect them...

This is going to cause problems...any recommendations....I was hoping to convert yzoers vdp/VGA project to the startkit
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infiniteimprobability
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Postby infiniteimprobability » Fri Dec 20, 2013 11:38 am

Yes they will - the node goes to both the LED and the pin (see schematic).

Green LEDs forward voltage is about 2V, so the 330R resistor will limit current to about 4mA. The pin will be able to handle that easily, so you will probs away with it.

Worst case, just remove the resistors!

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