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Mahmood Elnasser
12/27/12 13:35
  12/27/12 13:42

Read: 1019 times

#189049 - Found it
Responding to: Erik Malund's previous message
As Kai pointed out above:
In ten ways to bulletproof RS485 it says:
6 Termination and Stubs
A common mistake is to connect a terminating resistor at each node a practice that causes trouble on buses that have four or more nodes. The active driver sees the four termination resistors in parallel, a condition that excessively loads the driver. If each of the four nodes connects a 100 Ohm termination resistor across the bus, the active driver sees a load of 25 ohm instead of the intended 50 ohm. The problem becomes substantially worse with 32 nodes. If each node includes a 100 Ohm termination resistor, the load becomes 3.12 Ohm.

Jeez this was my mistake, I added a termination resistor on each node, should have read this app note again and not relied on memory!.

List of 13 messages in thread
RS485 supply voltage      Mahmood Elnasser      12/26/12 12:00      
   Could the data rate be a problem?       Richard Erlacher      12/26/12 14:12      
   5V      Erik Malund      12/26/12 17:17      
   No!      Kai Klaas      12/27/12 06:24      
      Strange!      Mahmood Elnasser      12/27/12 10:56      
         stubs?      Erik Malund      12/27/12 11:38      
            Found it      Mahmood Elnasser      12/27/12 13:35      
               I made $$ on that one      Erik Malund      12/28/12 10:22      
   How to Protect ?      Satish S Munot      01/09/13 23:32      
      Use MAX3430      Oliver Sedlacek      01/10/13 01:49      
         Or the LT1785...      Kai Klaas      01/10/13 05:10      
      MAX485      Satish S Munot      01/10/13 07:43      
         low      Erik Malund      01/11/13 13:41      

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