hi...
I have an RS232 db9 with female on one side and male on one side..the female is connectd to the PC and the male is connected the 89c51 kit (with max232).
My doubt is that 2 pin of female should be connected to 3rd pin of male or to the 2nd pin of male??
how do we check whether data is passing through the rs232 using a multimeter??
Is this following assumption right?? female rs232 --- 2-tx 3-rx male rs232------ 2-rx 3-tx
The TX pin of PC serial port always shows a negative voltage and u can check it out at pin no.3
without connecting anything the RX pin of PC,i.e.,no.2 shows zero voltage.
when you connect your male connector to the PC with the other end connected to the board the pins TX and RX shows negative voltage.....if you get these voltages,your configuration is right.
your assumption is absolutely right you can check the voltage variation on the multimeter where without data transmission there will be negative voltages on two pins (TX,RX)......
when you transmit or receive data you get RS-232 levels on the connector ..... The RS232 levels can vary from 3 to 12V(positive or negative)
"without data transmission there will be negative voltages on two pins (TX,RX)"
As you said originally, this only applies when the two devices are connected together - when the Rx is "open-circuit", it will show no voltage.
There may also be voltages on other pins (the control pins).
"when you transmit or receive data you get RS-232 levels on the connector"
This is true, but you are unlikely to see anything meaningful on a multimeter - the bits change far too fast for that! You really need an oscilloscope for this.
ya what you said is right scope helps a lot but even in multimeter also you can observe the variations.
Yes, you may be able to see some "variation" - but what useful information can you deduce from it?