Digital signal monitor - please help

Meepo

I'm trying to monitor asynchronous serial commands sent from another project, so I'm trying to use a HomeWork Board as a sort of oscilloscope. Here's the code I'm using, which doesn't work:

' {$STAMP BS2}
' {$PBASIC 2.5}

op8 VAR Bit
op9 VAR Bit
change VAR Bit
p8 PIN 8
p9 PIN 9


DEBUG CR
INPUT 8
INPUT 9
change = 0


DO

DO UNTIL change=1
IF op8 <> p8 THEN change=1
IF op9 <> p9 THEN change = 1
LOOP

op8 = p8
op9 = p9
change = 0


IF op8 = 1 THEN
DEBUG " I"
ELSE
DEBUG "I "
ENDIF
DEBUG " "
IF op9=1 THEN
DEBUG " I"
ELSE
DEBUG "I "
ENDIF
DEBUG CR

LOOP

What am I doing wrong? Basically I want to tilt my head to the right and read the data stream. As far as I can see, I shouldn't get a readout until either 8 or 9 changes, but I keep seeing the same signals repeated, and though I know the device I'm monitoring is sending the correct commands, I'm not seeing these commands displayed...

Vern Graner

Meepo said...
I'm trying to monitor asynchronous serial commands

<snip>
Ok so monitoring a serial stream seems to be the ultimate goal of the exercise, not so much the troubleshooting of the BSII code. [noparse]:)[/noparse] If so, you might want to have a look at this very useful free program:

http://www.serial-port-monitor.com

I've used it very successfully to capture data streams going to/from my PC and an external serial device (such as a uMP3 or a Soundgin etc.).

Hope that helps.

[noparse]:)[/noparse]

Vern

PS: I don't have any affiliation with the above company, I just found them in a google search a while back and thought I'd share my experience.

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Vern Graner CNE/CNA/SSE    | "If the network is down, then you're
Senior Systems Engineer    | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
http://www.txis.com        | is up, then we obviously don't need
Austin Office 512 328-8947 | you, so why are we paying you?" ©VLG

Meepo

I may download that program, but for my own benefit, I'd really like to know what is wrong with the above code...as fasr as I can see it should work, but doesn't...

Franklin

try a label and a goto on the outside loop. Also what "does not work"?

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- Stephen

allanlane5

What do you have on the inputs of P8 and P9? If it 'floats' (in other words, doesn't give you a hard +5 or a hard 0 volts) then P8 and P9 will trigger 'randomly' (actually, at a 60 HZ rate, there's a lot of 60Hz 'noise' an unterminated input pin will pick up).

Phil Pilgrim (PhiPi)

Have you considered the relative baud rates of the external system versus DEBUG? Each time DEBUG outputs, it prints six characters; and when this happens, your program is deaf for more than 6mS while it does the output. (6 characters * 10 bits/char / 9600 bits/sec = 6.25 mS.) What's coming from the external system during this time that you're missing?

-Phil

Meepo

Pin 8 is the clock and pin 9 the serial line. My first post describes the problem. I hadn't considered the Debug pause, that may explain why I keep getting the same signals outputted, when it should only print a change. I'll try a signal buffer, as well as putting a delay in the source program to slow down the output. I'm not sure of the relative baud rate, though it's probably slower than 9600.

Phil Pilgrim (PhiPi)

It needs to be considerably slower than 150 baud for your scheme to work.

-Phil

allanlane5

For $200 or so, the ANT-8 makes a really nice 8-channel digital capture logic analyzer. That might help you more.