hai all,

I have system that use PC and uC. 1st PC control the system using VB then send data to uC using max232to print out some note at LCD screen. The main problem is max232 only cover short distance. I have heard people said to use max485 to get more distance in data sending, but the problem is, it difficult to understand the circuit that i attached. Beside that i also want to know if max232 and max485 will interface together to make far connection. If possible could someone help me with full circuit connection between PC and uC. Thanks.......

 

The diagram is telling you to use twisted pair for wiring. This helps keep noise down.

Wire it straight through. Same wire on top of both ends.

 

You could use a MAX485 to extend the range. And then use a MAX232 after the MAX485 (on the PC side) In order to convert the signals into RS232. Or use a dedicated 485 interface card on the PC. Most of RS485 cards behave as serial port. So they can be programmed in the same manner

 

By the way, what the different between max232 with rs232 and between max485 with rs485?????????

 

RS232, and RS485 is standards defining the electrical characteristics of serial drivers and receivers in digital systems. MAX485 and MAX232 are common ICs used as interface elements then using the latter standards. The are also know as level translators. You can not tie neither RS232 or RS485 signals directly to say a microcontroller

 

ok back to topic.....

how to make connection between rs232 and rs485????

 

I dont think you can, directly. You would need a MAX232 IC to convert the RS232 signal to a common stream, then wire it to a MAX485. The MAX485 chip will convert the stream to RS485..and vice versa.

 

A link using a single MAX485 at either end will only give you one data signal and one direction, unless you add extra software to enable and disable the drivers at either end.

If you want a 'transparent' extender, you will need at least two pairs, one for TDX and one for RXD. You may also need another pair or two for handshake signals.

You need a ground connection between the two ends of the link as well, as the 485 link can only stand a small amount of ground voltage difference before it stops working.

If you go with the transparent setup, you could use ICs such as the DS8921 which have one driver and one receiver in an 8 pin package.

The link cable could be Screened CAT5 ethernet cable, or normal cat5 plus a ground.
(Or, if you need less than four signal pairs, uses the spare pairs as ground).

 

www.max485.com sells converters plus schematics are on their site.

 

Max485.com has the best prices on the 'net!

However, they can be hard to get a hold of.

Do you have any aditional info on the RFID?

 

If you download this data sheet http://datasheets.maxim-ic.com/en/ds/MAX1487-MAX491.pdf
You will find out that using some full duplex variant is probably better for your project. See selection table. Because what I meant, was that you should look at MAX485, and MAX232 types of circuits.