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b.p.m.
05-09-2008, 02:21 AM
hey everybody
I'm trying to figure out if I fried my prop (dip 40) or just can't get the RS232 circuit
working.
Question 1: I miswired the power pins temporarily, now I'm not sure if I fried my prop
chip. I measured the resistance across vss and vdd in both directions and came up with
about 1 meg ohms in either direction. That seems pretty high for a LSI chip like the prop.
Any ideas on how I could test my Prop or what to check with a DMM? I don't have access
to an o'scope or anything beyond a couple of cheap DMMs.
Question 2: I've tried both the 2 transistor and 3 transistor versions of the RS232
interface circuits. Obviously I have not got either working. Has anyone got any ideas
on what I can modify (ie, resistor or capacitor values) or an alternate solution. I thought
about breaking down and ordering the MAX3232, but that's at least a two week wait
and more than a few bucks after S&H and customs fees. I can get various versions of
the MAX232 (5V version) locally and wondered if I can adapt this via a couple series
resistors to work with the prop.
any help would be appreciated.

b.p.m.

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"Can't sleep, clown will eat me."
Bart Simpson

Post Edited (b.p.m.) : 5/8/2008 8:40:59 PM GMT

b.p.m.
05-10-2008, 02:17 AM
A quick update;
Through the help of Harrison at freenode/#propeller site I tested my prop via a led
hooked up to SCL line and learned it's not fried (thank goodness).
I guess that brings me back to the RS232 circuit. I'm going to juryrig some leds and
a pulse capture circuit to try and pin down the problem. About using a
MAX232 with a 1K series resistor on the prop's Rx line, is this viable?
ANY ideas about alternate setups would be greatly appreciated.

blake

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"Can't sleep, clown will eat me."
Bart Simpson

Mike Green
05-10-2008, 04:27 AM
The 3 transistor circuit shown on the Propeller website does work as long as the DTR line is active since this supplies a negative voltage for the transmit line (to the PC). You could use a MAX232 if you put a 1K series resistor in each line from the MAX232 to the Propeller.

b.p.m.
05-10-2008, 07:21 AM
Thanks for the info, Mike. Especially about the DTR line; I'll keep that in mind
while trying the 3 transistor RS232 circuit again.

blake

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"Can't sleep, clown will eat me."
Bart Simpson