MAX232 Connection

[ZERS]

Hi,

I found several schematics on the net regarding the connection of a max232 to a pic.

As for its V+ pin is concerned, somtimes it is connected to +5V, sometimes to ground (both through a decoupling cap) whilst its V- pin is always connectd to the ground

Why ?

Do I connect V+ to ground or +5V ? What is the difference ?

PS : I will use the MAX232IN

Regards

[paulb]

I didn't see the MAX232IN listed in the data sheet, but connections can be found there see p. 17:
http://pdfserv.maxim-ic.com/en/ds/MAX220-MAX249.pdf
V+ and V- are outputs. V+ is connected to a cap, which goes to Vcc. V- is connected to a cap which goes to ground. Vcc is the power supply input.

[ZERS]

Originally posted by paulb
V+ and V- are outputs. V+ is connected to a cap, which goes to Vcc. V- is connected to a cap which goes to ground. Vcc is the power supply input.

Yes I know that. But once again I've seen schematics where both V+ & V- are connected to ground (trough a cap) !

Why ?

[philbyx]

Hello Zers

Those EIA RS232 adapters have to convert 0, 5V ttl to +12/-12 rs232 levels (same as V28 CCITT).
You connect +5V on Vcc pins, and it is all.
In the circuit, you will find a voltage doubler and a voltage inverter in order to output the good levels.
You just have to connect decoupling devices (Capacitor) on the pins V+ and V- . Those tension are internal and permit the +/-12V on the output.

Philippe

[ZERS]

Originally posted by philbyx
Hello Zers

Those EIA RS232 adapters have to convert 0, 5V ttl to +12/-12 rs232 levels (same as V28 CCITT).
You connect +5V on Vcc pins, and it is all.
In the circuit, you will find a voltage doubler and a voltage inverter in order to output the good levels.
You just have to connect decoupling devices (Capacitor) on the pins V+ and V- . Those tension are internal and permit the +/-12V on the output.

Philippe

salut philby, comme on se retrouve

[jaycee]

It is a charge pump converter to convert 5v into +/- 10v. Vcc and GND are the power supply pins. The others are internal connections for the charge pump doubler, inverter, etc.

Just do what everyone else does (or should be doing!) and use the schematic shown in the data sheet Incidentally Maxim now have a chip to do this job that needs no external capacitors.

[macboy]

Yes I know that. But once again I've seen schematics where both V+ & V- are connected to ground (trough a cap) !

Those schematics are incorrect.
Connect the device as in the datasheet from Maxim.

[ZERS]

Originally posted by macboy

Those schematics are incorrect.
Connect the device as in the datasheet from Maxim.

All right sir
here si the datasheet of MAX232IN