| ??? 11/19/05 05:14 Read: times |
#103905 - Helpful Responding to: ???'s previous message |
Erik Malund said:
Chris said:
I was always talking about the 3 resistor method of failsafe biasing, not any particular 485 driver IC "special feature". how was I to know? Because I used the phrase "fail-safe BIASING". By inclusion of the word "BIASING" I would expect someone with your obvious knowledge to realise that I would be BIASING the lines. From what I have seen the fail-safe feature of some 485 receivers does not bias the line but rather gives a defined output at zero volts (+/- some margin). Please correct me if I am wrong. Erik Malund said:
That is not RS485, that is J1708 That was a very helpful peice of information. Thank you. For the benefit of others, National Semiconductor has AN-915 that discusses J1708. Erik Malund said:
If you do not go "master permission" you WILL end up in collision detection reather than collision avoidance. [snip] A busy J1708 bus is handling so many collisions that it severely hampers throughput. [snip] The code to handle J1708 is about 10 times the size of a RS485 master. Thanks for your concern, but again, if you read my words carefully, you will see that I do not desire an "anyone can transmit, anytime" system but rather a method of "slave discovery/enumeration", which will have collisions only in very controlled circumstances. |
