Hello guys. i am new here.
has any one worked with max 232 I.C ? i am doing a project on serial communication, the microcontroller circuit is working well, but having issues with the max232 I.C.

 

What seems to be the trouble?

 

What seems to be the trouble?

the OP is having troubles expressing troubles s/he is having.

 

Thanks Sensacell.
My objective is to control external load from my P.C using the hyperterminal interface.
i have observed all the necessary rules in its connection, but still not working.
tying to upload the schematics here, but dont know how.

 

This is my schematics. the only modification is that is used 10uf cap instead of the 1uf cap in the schematics.

 

Am open to suggestions.

 

Hi.

First thought:
Change your caps. I use 0.1uF.

Second thought:
Upload your schematic and a picture of circuit. Include the code as well. Also a description of what you want to happen, and what is actually happening.

 

View attachment 117397

This is my schematics. the only modification is that is used 10uf cap instead of the 1uf cap in the schematics.

Your schematic is so tiny. Can you post a larger one for us old folks?

Are you certain it is the MAX232 that is the issue? What have you done to diagnose the issue? Are you certain data is getting to the chip?

I use 1ufd tantalum cap all around. I think 10ufd is going to be too large. And you should have a .1 ufd as a bypass cap on your VCC.

 

Hi.

First thought:
Change your caps. I use 0.1uF.

Second thought:
Upload your schematic and a picture of circuit. Include the code as well. Also a description of what you want to happen, and what is actually happening.

Nerd is right. Your caps may be too large, that happened to me once. Are you really using the original MAX232 chip?
Other brands, such as the SP232A, require the use of much smaller capacitors, like the 0.1uF that has been sugessted. Although I've seen cases for 1uF too.

Check your chip's original datasheet.

 

Nerd is right. Your caps may be too large, that happened to me once. Are you really using the original MAX232 chip?
Other brands, such as the SP232A, require the use of much smaller capacitors, like the 0.1uF that has been sugessted. Although I've seen cases for 1uF too.

Check your chip's original datasheet.

Why do you think the caps are too large? It seems to me that over-large caps just reduce the ripple and output impedance.

The spec sheet gives _minimum_ capacitance values since this is normally what designers are interested in. A large capacitor value will slow the turn on time of the MAX232 but an extra several hundred micro seconds won't be a problem unless data is transmitted very soon after power up.

In other words, I don't think the 10 uF is too large no matter which variation of MAX232 is used.

 

To work out if the MAX is working just short the RX and TX pins and connect to a computer. Make sure local echo is turned off in your terminal software and try typing. Do the characters come back?
This process will take your microcontroller out of the picture.

 

Why do you think the caps are too large?

I have no idea, I don't know the innards of those chips, and don't know how exactly they raise their outputs to the standard RS232 level.

All I know is that I once had a headache when I tried to use the SP232A for the first time, and I couldn't make it work until I read the datasheet and changed the caps to the recommended values.

 

I have no idea, I don't know the innards of those chips, and don't know how exactly they raise their outputs to the standard RS232 level.

They use capacitor charge pumps similar to the ICL7660. No magic.

 

Long ago I once used 22μf tantalum with OK results.
Max.

 

They use capacitor charge pumps similar to the ICL7660. No magic.

I wonder then, if the caps were so large that they wouldn't have enough time to acquire a charge high enough for the pump-circuit to function properly... or is that irrelevant?

 

Thanks guys for your comment.
i will get 0.1uf cap at the electronics store. should it be a tantalum or electrolytic cap ?
i have attached the source code and the enlarged image of the schematics.
is there anything wrong with the source code or schematics?

 

Hello,

Wich version of the MAX232 are you using?
The MAX232 needs other capacitors as the MAX232A.



Do you have pins 2 and 3 of the DB9 correct?
http://www.hardwarebook.info/Serial_(PC_9)

Bertus

 

i used MAX232 which according to the datasheets needs 1uf electrolytic cap. i have tried it with 1uf, but still not working the way it should work

 

Thanks guys for your comment.
i will get 0.1uf cap at the electronics store. should it be a tantalum or electrolytic cap ?
i have attached the source code and the enlarged image of the schematics.
is there anything wrong with the source code or schematics?

View attachment 117458

Tantalum. Don't know if you will get electrolytics that small.

Do you have a scope? If so, can you see data coming into the MAX?

And you have an electronics store nearby???

 

is there anything wrong with the source code or schematics?

View attachment 117458

Just as a real quick look. I would not use interrupts till you get things started. I would just poll the register. You are just adding to your misery right now. Get the thing working then you can add interrupts.

Have you looked at the peripheral library? Or better yet the Micro Chip Code Configurator (MCC)? Sure makes the job a whole lot easier.