MAX232 output problem? (solved)

[rprodrigues]

max 232 problem

Hi all,

I have been facing some problems with outputs from MAX232 ICs.

I am trying to use an MAX232, a PIC (18F2620) and some other stuff in a circuit to receive data from a GPS by means of an software USART (at 4800 bauds). To do it, I connected one of the pins of the PIC in use do detect the H-to-L variations of the signal do receive. This H-to-L variation is used to trigger the init of the process to receive the serial data.

The problem I realized is that the MAX232 output pin, when there is a voltage of 0 to -12V at the related input PIN, oscillates with a frequency of about 43 kHz.

Is it a regular behavior of the MAX232N IC or it may be any other problem with my circuit?

I have already tested several units of the MAX232N IC, even out of the my circuit, and the output always oscillates when inputs of 0 to -12V are applied.

In my opinion, it is not a problem of my circuits since I am following the manufacturer "typical operation circuit".

Any help would be appreciated,
Rodrigo

 

[FvM]

max232 circuit

In my opinion, it is not a problem of my circuits since I am following the manufacturer "typical operation circuit".

Most likely not!

 

[davidgrm]

max232 not receiving

Put a capacitor across the Max 232 supply line. A value of about 10u should do. I seem to recall this is the recommendation in the data sheet.

 

[FvM]

max232 problem

From the observation, the capacitor at -12V is missing or not connected correct.

 

[manish12]

max232 not working

To do it, I connected one of the pins of the PIC in use do detect the H-to-L variations of the signal do receive. This H-to-L variation is used to trigger the init of the process to receive the serial data.

The problem I realized is that the MAX232 output pin, when there is a voltage of 0 to -12V at the related input PIN, oscillates with a frequency of about 43 kHz.

as it is related to the serial data coming from gps module , keep serial int always active , if any data come on it , it automatically goto the int vector routine.

it is just possibility, it may be wrong !

 

[muralicrl]

is max232 damaged

Hi,

See the attachment, which is a application note on MAX232. You check the design with this.

If you need more details, contact me.

Regards,

N.Muralidhara
CRL-BEL

 

[rprodrigues]

serial pic max232 always sending problem

Hi,

See the attachment, which is a application note on MAX232. You check the design with this.

If you need more details, contact me.

Regards,

N.Muralidhara
CRL-BEL

Hi all,


Thank you for every one who gave me any direction.

Dear davidgm,

I realized that I should had put an capacitor between the pins 2 and 6 of the MAX232 IC.



rprodrigues

 

[Duby]

max232 + 12 v circuit

Hi!

I have question about MAX232N..... If I put +10V (-10V) to pin R1IN should I aspect 0V (5V) at pin R1OUT ? ? ?

..... because I read 1V (0.7V) ... which is not in PIC Level response... thx.

 

[FvM]

If I put +10V (-10V) to pin R1IN should I aspect 0V (5V) at pin R1OUT ? ? ?

Yes, exactly. If you see an intermediate voltage, R1OUT maý be loaded inappropriately, MAX232 supply is missing or the chip is damaged.