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RS-485 interface

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New Member
I need some help. I need a RS-485 driver to interface between a computerized timing system, and a PIC. It is one-way communication, signals from the RS-485 port need to be read on the PIC. Signals that are sent are just 2 digit numbers.
Doing a search for RS-485 drivers comes up with way too much information for me, I dont know which driver will suit my purposes.



New Member
I know a driver that works with Windows 95 and 98:
- Look at http://www.integrityusa.com/downloads.asp
- Download RS485NT.zip and RS485_95.zip files

RS485_95 works very well in Windows 98. It controls RTS line without delay that you explain.

I have been trying to use RS485NT at Windows XP with Visual Basic 5.0 but it doesn't work.

Could someone help me ?

I need a FREE driver, or dll, or ActiveX that control RTS line automaticaly at Windows XP.


New Member
RS485 interface

Take a look at ...
Strip away the MAX232 chip and just use the 75176, an RS485 driver.

As your PIC will be throwing 5v (ish) signals around;

For recieve ...
The 75176 pin 1 (Rx) will connect directly to the PIC.
The 75176 is wired to permanently recieve everything on the RS485 bus (pin 2 held low)

For transmit ...
Connect to the 75176 pin 4 directly for transmit data. The enable pin (3) can either be taken high for the duration of the transmission or wired high if you never need to recieve.

Programming for the PIC ...
Use any old RS232 routine that suits you !

This 75176 is STATIC SENSITIVE - there is another chip which isn't static sensitive but I forget its number and have had no problem with this IC.


New Member

i also have problems with this setup...

for example??

do i need to use inverted comm or true??

how much has to be the resistor between pin 6 and 7..?? Rt in the data sheet..

will take a look at the shemes etc..



Active Member
I always use this configuration, work well with cheap CAT5 UTP cable upto 400m. The 120ohm need for cable end, value depend from cable impedance.



New Member

how do you config the pic? i mean

wich speed do you use? do u use inverterd or true mode?

for example 9600,8,n,1 ???

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