TV Output on P28-P31?

Philldapill

I'm just curious if there are any problems using the TV output object with pins 28-31. I know these are used for the eeprom and programming purposes and I'm not sure if it can be done. If it can, are there any precautions to take? I'm making a PCB that will use pins 0-27 as general purpose IO pins, but I can't fit the last four pins on it for direct access. So, I figured I would just add an RCA jack on those last few pins and not let them go to waste.

Oldbitcollector (Jeff)

While I haven't tried this, (and perhaps a breadboard run of this configuration would answer questions.)
I'm pretty sure that the resistor DAC for the video would create some issues for you.
It's generally accepted that you can use the programming pins *if* what you are connecting is not
attached while they are in use. A switch in the circuit could give you isolation, but
then you would have the added physical step every time you program it.

OBC

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Phil Pilgrim (PhiPi)

The resistor network will most certainly interfere with the SD line to the EEPROM, since it relies on a 4.7K - 10K pullup resistor for a logic "high". Any series protection resistors in the programming device will also be affected.

No, this is definitely something I would not do.

-Phil

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Philldapill

Ok forget the eeprom pins. How about using the TX and RX pins, plus pin 28? i.e. IO 27, 28,29? I'm guessing when you talk about the programming device, you mean something like the prop plug? I can live with devoting one "general purpose" pin to the TV, plus the TX and RX lines since I'm not using them.

Baggers

You have to start the tv on every 4th pin, so at 24, or 28.
Btw, why does it have to be 28 dedicated to general purpose, why not 24? Hybrid and Hydra use pins 24, so it would be compatible with their tv drivers with no chanes other than clock speed.
In face, why add TV at all, since you're dedicating 28 to GP, people can use their own layout, and can use 12 like protoboard/demo board, or 24 like Hybrid and Hydra.

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Philldapill

I'm trying to make a simple board with all the available pins out front. This will plug into a 30 pin breadboard, so I'd like to have as many pins out front as I can. I'm just trying to find a use for the last 4 pins if possible...

Phil Pilgrim (PhiPi)

Pins 28 and 29 are the EEPROM pins. TX and RX are on 30 and 31, respectively. The logical use for pins 28-31 is serial and I2C interfacing, not video.

-Phil

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Baggers

If you want a use for the last 4 pins, like Phil says, let them be their current use, that way, you won't affect anything.
Also, if you're putting it in a 30 pin breadboard, then bring 30,31 down in place of 28,29, that way, you can have rs232 on you're board.
Another thing, Won't you want something like Vss and Vdd bringing to the 30pins? or at least Vss?

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Philldapill

Yeah, right now, here is what I have. I've attached a screen shot of the PCB in eagle. The top most pin on the left side is Vdd, below that is Vss, and below that is IO 0 of the prop, then IO 1, etc. all the way down to IO 27. So I have the power pins at the top, then all the I/O pins below that. It's a fairly neat and compact setup, but I'm sure I could further optimize it. A lot of holes to be drilled, but only 2 jumper wires needed, which aren't shown because they are on another layer.