i m using RS232 to communicate with my instrument, now i would like to change the RS232 point to RS485...

i confuse with the point that i should use in RS485...

the point that i use in RS232 are TxD,RxD,RTS,CTS

but inside RS485 got TxD+,TxD-,RxD+,RxD-,RTS+,RTS-,CTS+,CTS-

which point should i use in RS485...

Thanks

 

You probably have a 4 wire RS485 full duplex. Data is transmitted differentially in both standards. I suggest you buy a converter or build one with a MAX202 IC.
Theoretically if the distance is short you may connect them straight it depends on the UART the devices have probably are 16C550 for older devices and 16C552 for new ones.
However the range of the RS485 standard has a common mode voltage Vcm that the driver and receiver can tolerate of +12 to -7 volts so +13 and -8 may not be understood.
This may help you understand:
http://www.bb-elec.com/tech_articles/rs422_485_app_note/overview.asp
This if you want to buy one converter:
http://www.axiomatic.com/rs232-485-isolation.html
I also recommend you this book:
Programming and Circuits for Rs-232 and Rs-485 Links and Networks

 

thanks a lot to your explanation...

i get wat u mean..

intinially i jus thought i only need to connect the wire Rx to Tx,that's all..

i misunderstand that there are differentially in both standards...

thanks..