Using Propeller pins 28-31 after boot-up

yarisboy

I've searched this forum but may not have used the correct search nouns. I'm looking for examples of usage for the subject pins. I'll need the rules for these pins before I can design I/O for them. Help.

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jazzed

yarisboy said...
I've searched this forum but may not have used the correct search nouns. I'm looking for examples of usage for the subject pins. I'll need the rules for these pins before I can design I/O for them. Help.

One thing I found out the hard way: never drive output bit OUTA[noparse][[/noparse]31] without a big value resistor if a PropPlug is connected. I broke my first PropPlug to heck doing that even with a 1K ohm resistor in series. I won't ever do that again on purpose, and I won't recommend any configuration.

Philldapill

If I remember correctly, pins 28/29 are used for the I²C eeprom. Since this is an I²C bus, you can use any other·I²C·compliant device on these pins - that·is not using the same address that the eeprom does. This really is great because in a project of mine, I used these pins for 3 accelerometers, and a temperature sensor... A total of 5 devices(including the eeprom) on only 2 pins!

The other set of pins, 30/31 are pretty much off limits if you ever plan on using the prop-plug in circuit. However, if you really need pins, you can pre-program your eeprom, drop it into your circuit, and use those pins just like normal. Just don't have anything connected to them if you use your Prop Plug at any point.

jazzed

If you want to use P29 for something other than I2C, you can drive P28 low after boot and the EEPROM will ignore P29.

Toby Seckshund

I have experimented, on breadboard, with some bi-lateral switches (4053) and have put the 2 wire KBD onto P28-29 after boot up. The switch over is done by a diode pump from the H sync of the 4 pin VGA. So as long as the drivers are started in the correct order it works. I am 90% finished on a pcb version so hopefully this will fire up over the hols.

Clusso's one wire drivers could be used and save a whole bunch of pins (I just wish I had a video monitor that had decent focusing)

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ManAtWork

Hello Yarisboy,

in my stepper motor controller design I use all propeller pins including PA28..31. You just have to be aware of the following limitations:

a) use PA31 as input only (conflicts with prop plug as Jazzed already mentioned)

b) if you use PA28..29 for something different than I2C bus be sure to never generate a start bit condition

Cheers

mctrivia

P28 and P29 i would recommend keeping just to I2C devices though as mentioned it is safe to use P29 for IO as long as P28 is low. If you want to put 16 EEPROMs on you can put 8 on P28/P29 like normal then on the last 8 hook them up P29/P28.

I would recommend using P31 as an input only and P30 as output only so as not to interfere with the propplug.

P29 is pulled high on all boards and most board designs pull P28 high also so if connecting switches make sure you connect them to ground. connecting to Vdd and pulling low would cause the pin to float between rails.

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WBA Consulting

I used P31 on a project I just finished for the clock line of an SHT11 sensor. It was used because I used a Propmodule1x1 and a 2 pin header fit perfectly in the location where P31 and GND were next to each other (yellow and black wires). The SHT11 sensor was not connected whenever I programmed the EEPROM, so I did not have any problems.

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