Prop programs but doesn't work
Jonathan
Posts: 1,023
Been a while since I played with the Propeller. I started with one I have mounted on a breadboard. It programmed but wouldn't do anything. At first I assumed that I had something wrong in the program. Looked and looked but saw nothing wrong. Then after programming a prop on a PCB board I made a few years ago and it working with the program I working on, I figured it must be a PLL failure. So I put a new DIP prop in the breadboard. Still not working. Then I thought maybe it is the crystal. I don't seem to have any 5mHz crystals laying around but I have a 3.57 mHz, at least it is marked 3.57. Still no no joy.
Any ideas? I will order some crystals, but would like to figure out what the heck is going on here.
Comments
Best to post a pic. Often we can see the problem this way.
If your program calls for a crystal oscillator, and you haven't provided a crystal -- or one at the wrong frequency -- it won't run properly, if at all.
What are the first lines of your main program?
-Phil
Phil, Cluso, so glad you guys are still here!
I am using a 5mHz crystal, both on my home made PCB and on the breadboard. I just tried a crystal that I unsoldered from a board and added legs to, still no luck. The following program runs fine on the PCB but not on the breadboard. It downloads just fine.
EDIT: I see the formatting of the code got trashed but it is indented correctly.
CON
_clkmode = xtal1 + pll16x
_xinfreq = 5_000_000
input = 0
output = 1
OBJ
pst : "Parallax Serial Terminal"
PUB init
dira[15] := output
pst.Start(115_200)
pst.clear
pst.home
wait_ms(2000)
pst.str(string("GPS Timebase..."))
pst.newline
pst.str(string("Version 0.1"))
wait_ms(1000)
repeat
pst.str(string("Testing,,,"))
pst.newline
outa[15] := 1
wait_ms(1000)
outa[15] := 0
wait_ms(1000)
Cluso, here is a picture:
You need bypass caps on both Vdd/Vss pin-pairs. It could be that, lacking both, the PLL got fried. It's a known failure mode from inadequate bypassing.
-Phil
Aha! Found the problem! Cluso, thanks for asking me to take a pic. Looking at it I noticed that the decoupling cap on the power pins on the left side was missing. Put one in and all is well. Sometimes it is the little things.
Well spotted Phil! We must have cross posted.