8255 problems

ThePenguinMaster

hey guys,

ive been having some problems running the 8255 driver on a propeller. i have all my lines connected and it is partially working. heres whats happening:

i put all of the 8255 ports into output mode, and i can read off of·portA perfectally! port B and C are un responsive. i would think it was my address lines A0-A1 buyt they are connected correctly.

when i try to output to c and read off of b, whatever i output from c appears on b, although there is no hardware connection between the two.

in my program, i am setting the pins via the setpins function, and then setting the direction. and then trying to read or write

the intresting thing is that when i set the ports to out, a can read in, and when i set the ports to in, a can output. i know that in the 8255 driver that they say this is backwards so they reverse it in the driver, so maybe this isnt true for some reason?

its a single 8255 connected to a propeller.. any help would be appreciated!

also sometimes i get weird readings from b and c, kinda like random flickering of 1's and 0's.

Beau Schwabe

Can you post a schematic and software that you are using?

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

ThePenguinMaster

yah i guess that might help! lol.. ill have to draw up a schematic, because right nowim keeping track of pins on a chart in a notebook, so a schematic might be a good idea. ill post the software and schematics tomorow because im not at hme right now. i dont know if this helps but heres a picture of the board.

deSilva

The 8255 is not assumed to run at 3.3V... If you are using a 82C55 this could run at 3.3V... However you need to put defined signals to all inputs. Is CS connected? Also I cannot see that Vdd is connected...

The two blue wires running from the programming connector... Do they source current to the middle rails, or do they draw current from it?

ThePenguinMaster

the two wires running from the programming connector to the rails give the rails power, also the orange wore on theright hand side supplys +5v to the 8255.

the cs is grounded out because it is my only 8255 on the bus.

the set of resistors on the lower left keeps the prop from frying when it recieves signals from the 8255 chip.

the wires running from the resistors to the 8255 have been re-done since this picture so theyre no so bundled up anymore.


also note that +5 is supplied to the 8255 running under the orange wires with the black wrapping on them. ground is connected through the rails.

bambino

Maybe no big thing, depends on how your switching between Read and write, but I would suggest using the CS line.
When you are setting up your data bus to input for a read, or output for a write, anything you do to the dira register for those pins could be interpreted as data. When in fact you've not touched the outa register yet. Look at the state of the RD and WR line at the time you are changing the the state of the dira registers, if they are in transition from low to high or vice versa that might be the problem.

ThePenguinMaster

Of coarse! *smacks head* why did i not check the only thing i did different than every one else in the world! lol. ill have to give that a try.

i guess i was thinking whils i was reading the datasheet that i wouldnt need the cs lines to run the chip. but of coarse until i get my own driver running, im using someone elses and i should fallow their directions for a reason. i have a 4 day weekend comming up so ill havce time to give it another go. ill let you guys know how it goes.