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nasbyc
Joined: 27 Apr 2009
Posts: 50
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nasbyc
Joined: 27 Apr 2009
Posts: 50
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 Posted: Fri Nov 11, 2011 6:02 am |
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| Ttelmah wrote: | | Differential busses, with twisted pair wiring, are _much_ more likely to be reliable with motors around. Even over the short distances involved, you _will_ have problems with single ended busses like RS232/RS423, and motors nearby |
I decide to try with rs485 by using max488. I noticed that it is a full duplex and 4 wire needed to connect one device to another A,B,Y and Z. Do I really need the physical twisted wires connecting them. Does it mean I have to use separate stripboard. About the pin:
pin DI connecting to TX (pic)
pin RO connecting to RX (pic)
The same configuration should be similar for master and all slave, am i correct? And by using hardware device (max488), I'm bit confused about which config do i need to use, either software uart or hardware uart. |
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temtronic
Joined: 01 Jul 2010
Posts: 9243
Location: Greensville,Ontario
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| Posted: Fri Nov 11, 2011 6:31 am |
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If you look at the MAX1487..491 datasheet, fig. 21 shows a 'typical half-duplex RS-485 network' which shows how to hookup your PICs to a network. Normally the TX and RX control pins are tied together so the PIC only needs 1 pin to work. The use RS232(...) has an option as to which pin does this.
You have to decide whether you want full duplex or half duplex mode. Most probably use half duplex, overall easier, fewer pins, smaller chips, etc. Tons of example code here and there as well.
Twisted pairs allow for better noise immunity.Typically you use 'CAT5' cables. One pair for signal, if half duplex, 2 for full duplex. The other 2 pairs are paired for power to the 'remote' PICs on the network.
Using the hardware UART allows for faster operation since you get to use ISRs and the UART buffers. In your case, since each PIC only is on one network, I'd use the hardware UART.
I'd use the MAX481 for your project, fastest of the chips, has 'control' pins, the choice for 1/2 duplex operation. |
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nasbyc
Joined: 27 Apr 2009
Posts: 50
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| Posted: Fri Nov 11, 2011 9:43 am |
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| Thanks a lot guys. Really apreciate all your help. What i need now is to buy the components and construct the circuit. |
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