DB 9 's 3rd pin giving negative voltage is it normal?

[haroon_tech]

hi,

i am developing a AVR atmega 16 board. in that DB9's 3rd pin giving negative voltage ..but in ckt from 3rd pin the diode placed then how diode will work to negative voltage?

can any body help me ...........

 

[betwixt]

We need more information. What is the 3rd pin supposed to do?
If it's an RS232 serial interface it is quite mormal for it, and other pins to have a negative voltage on them. The spec is optimized for signalling with voltages of +12V and -12V although the normally acceptage range is very wide, typically +/- 3V up to +/-30V.

Brian.

 

[bigdogguru]

As Brian indicated, if the DB9 is a RS-232 connection, pin 3 is TX, pin2 is RX. Large negative voltages are normal in the RS-232 Protocol.

Here's a pinout of a RS-232 DB9:

RS232 DB9 pinout

and a discussion of the RS-232 Protocol:

Signal Characteristics of RS-232

 

[ckshivaram]

what is your application, Is it used for serial communication or for any other modified protocol or application, put your circuit and what diode are you speaking about.......

 

[haroon_tech]

hi,
i am developing an atmega32 development board ..i have attached my schematic ,




in that schematic i am using only programmer part for AVR .

in the ckt DB9 3rd pin is directly going to anode of diode then to transistor via a resistance. i doing it on bread board ..

please can you tell me this programmer ckt is correct or not ?..........

my problem is that DB9 3rd pin is giving negative voltage so it is connected to anode of diode in ckt so diode wont work for negative supply.............. then how it works for programmer mode.......................

 

[bigdogguru]

Actually pin3 in the DB9 is going to the R1IN pin on the MAX232 as it should and Pin2 in the DB9 is connected correctly to the T1OUT pin on MAX232 for RS-232 communications. The remaining pins are ground and what looks like a SPI serial programming interface.

Are you sure you're not turned around looking at it from the wrong direction?

---------- Post added at 05:48 ---------- Previous post was at 05:41 ----------

Checkout the datasheet section on SPI programming:

ATMEGA32/L Datasheet