MAX Pain!

[TheAnimus]

Ok, basically i've wired up the bob standard MAX232CPE circuit.

The PIC talks to the MAX, the MAX level changes then the PC.

Datasheet circuit, all as normal, as i must of done hundreads of times before. Only thing is, this one dosen't play properly.

The output of the PIC is perfect, i get just the trace you would expect on the scope, at a loverly 5v.
This is true on the input of the MAX, but on the output i get ZIP, nothing nadda.

So i remove the PIC (which can recive from the PC fine) and then put a peice of wire in teh socket, from tx to rx, and, it works fine, that is to say, both conversions the max does perfectly.

So i put the PIC back in, and put a 100k resistor in series with the scope, to make sure that there was some current there on the output of the PIC's TX pin. Of course there is, and its perfect, so i remove the PIC again, and start strobing the input to the max, and it works perfectly.

The max has +10v and -10v where it should, and looks fine.

The PIC is working as it should too.

This is doing my nut in, as i type this we are getting another max232CPE and PIC16F870, i will post the results of those

The only thing i can think of, that makes this differn't from my standard 16f870 interface with PC via rs-232e over max232cpe, is the fact i am using only 300baud?

But this i can't see been a problem, as when i short RX n TX on the "TTL leveled" side of the max, it works fine.

Ideas?

 

[Nigel Goodwin]

Ideas?

Only that you're probably doing something incredibly simple wrong, and it's so simple that you can't see it. If you keep looking at it, it may suddenly hit you what's wrong :lol:

 

[TheAnimus]

so far 4 people have checked the circuit.

I think your probably write thou, but it does look exactly like the datasheet and standard circuit, just added yet another tantalum accross the power, and thats not helped.

 

[TheAnimus]

still waiting for the fresh max232 n 16f870.

But now i have found somthing strange.

When i don't have the PIC in its socket, the voltages on the MAX232CPE's pins 2 and 6 are correct (rather close enough at 10v and -9v) but with the PIC in, they drop to 5v and -0.48v respectivly.

Any Ideas?

 

[StupidDum]

Probably supply current is insufficient or somehow the circuit is shorted, or pin connected wrongly

 

[TheAnimus]

one of the caps connected to one of the portb pins, not my fault *honest*

took 4 hours, lesson been, get someone who has good eye sight to look at your board

 

[Nigel Goodwin]

one of the caps connected to one of the portb pins, not my fault *honest*

took 4 hours, lesson been, get someone who has good eye sight to look at your board

I told you it would be simple :lol: