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Ask RS485 Trouble ?

Hi, I have built RS485 communication for 11 AT89S51 microcontrollers. Consis

1 master and 10 slave nodes. I use SN75176BP for RS485 driver. Al microcontrollers connected using UTP Cat-5 Cables in a bus : Safe bias resistor-SL1-SL2-SL3-SL4-SL5-SL6-MA-SL7-SL8-SL9-SL10-resisto terminator. From SL1 to SL7 connection works fine, but from SL8 to SL10 still canno connected. Total length of cables about 500m. At one end of cables i giv termination resistor 120ohm and the other end using safe bias resisto Vcc-750-120-750ohm-Gnd. I'm using baudrate 9600bps for communication. The protocol is simple, each 100ms master will send an address. Slav would response if they address send by master with send a few byte of dat to bus. These data will be read by other slave. What's wrong with SL8 to SL10? Can you give me a solution for thes trouble? Thanks for your attention.
Reply to
TR6
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Normally this should work. I've run similar networks at 96-125kbps. Have you checked the signals with an oscilloscope?

Meindert

Reply to
Meindert Sprang

"TR6" schreef in bericht news:-YOdnU6Ls7wfQW_ZnZ2dnUVZ snipped-for-privacy@giganews.com...

First thing to do is hook up an oscilloscope and see what the signal looks like, at the receiver end. Measure the amplitude.

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Thanks, Frank.
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Reply to
Frank Bemelman

Do they all have the same ground reference?

regards, DR

Reply to
Darcy

If address selection 1s done by software, can slaves 8 to 10 receive when placed in the 1 to 3 hardware positions?

Section isolate into hardware/software.

Don...

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Don McKenzie
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Reply to
Don McKenzie

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