SX28 heating up
Keith M
Posts: 102
Happy Saturday night to you!
I'm using the SX28 protoboard(www.parallax.com/detail.asp?product_id=45302) and have some I/O pins running directly to an external floppy drive. While my future prototype versions will include a current-limiting resistor for protection of the SX, none are currently (note the pun, haha) in place.
I've attached the recommended interface schematic from the specs of the drive, obviously the host side is the SX.
I've noticed that normally when I wire something incorrectly is when I have heat related issues. For instance, I'm shorting something to ground, like a lead that is asserted high, etc. Note that the SX28 is getting almost too hot to touch when left on for more than 20 minutes.
I am using an external pullup on the READDATA line, but plan on using the weak internal pullups for the other signals. Most of them are not critical, and a wide pulse, or slow rise time etc isn't important.
I am inclined to think that it is the OUTPUT's towards the SX that are causing the problem. I seem to recall I fixed a heat issue there by simply putting a resistor on the single lead (at the time) that was outputting towards the SX.
I've been using 220 ohm resistors which seem to work good enough. Without a custom PCB (which is the eventual goal), working with a solder-based protoboard is sort of a pain in the butt to add or have a lot of components, like multiple resistor packs, etc. I have the solderless version as well, but the space is a little too limited. My custom PCB isn't too too far in the future, so going to a larger/different board is a waste of time (IMHO).
While I know what the fix is, I'm looking for a better explanation of what is happening here, and also advice for any additional requirements that I've missed due to my lack of good electronics experience.
I appreciate your time to take a look at this.
Thanks
Keith
P.S. While I don't have a current schematic, high res pictures are available below
www.techtravels.org/amiga/newfloppyfrontbig.jpg
www.techtravels.org/amiga/newfloppybackbig.jpg
I'm using the SX28 protoboard(www.parallax.com/detail.asp?product_id=45302) and have some I/O pins running directly to an external floppy drive. While my future prototype versions will include a current-limiting resistor for protection of the SX, none are currently (note the pun, haha) in place.
I've attached the recommended interface schematic from the specs of the drive, obviously the host side is the SX.
I've noticed that normally when I wire something incorrectly is when I have heat related issues. For instance, I'm shorting something to ground, like a lead that is asserted high, etc. Note that the SX28 is getting almost too hot to touch when left on for more than 20 minutes.
I am using an external pullup on the READDATA line, but plan on using the weak internal pullups for the other signals. Most of them are not critical, and a wide pulse, or slow rise time etc isn't important.
I am inclined to think that it is the OUTPUT's towards the SX that are causing the problem. I seem to recall I fixed a heat issue there by simply putting a resistor on the single lead (at the time) that was outputting towards the SX.
I've been using 220 ohm resistors which seem to work good enough. Without a custom PCB (which is the eventual goal), working with a solder-based protoboard is sort of a pain in the butt to add or have a lot of components, like multiple resistor packs, etc. I have the solderless version as well, but the space is a little too limited. My custom PCB isn't too too far in the future, so going to a larger/different board is a waste of time (IMHO).
While I know what the fix is, I'm looking for a better explanation of what is happening here, and also advice for any additional requirements that I've missed due to my lack of good electronics experience.
I appreciate your time to take a look at this.
Thanks
Keith
P.S. While I don't have a current schematic, high res pictures are available below
www.techtravels.org/amiga/newfloppyfrontbig.jpg
www.techtravels.org/amiga/newfloppybackbig.jpg
Comments
It sounds to me like the SX is trying to drive the pin high when your shorting it to ground.
Even if you have a pullup resistor, if your shorting the line directly to ground, (with no resistor) then your draining all the current out of that pullup resistor, and the sx too. IF your shorting a line to ground, i'd suggest you use a 470 ohm resistor to short lines to ground. (its less than your pullup resistor, but still limits the current)
Directly shorting anything to ground or to vcc is generally a bad idea... And this is prolly why your sx is getting hot. If I were you, I wouldn't use that sx that over heated, its timing will prolly be off from now on. You can try it tho...
Good luck.
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Meh. Nothing here, move along.
Thanks