| ??? 09/14/06 17:57 Read: times |
#124320 - biassing Responding to: ???'s previous message |
Erik Malund said:
Apart from this, the real headache is biasing in a ever extending RS485 network. Do you have any automatic biasing system solution as bus gets longer in time? I do not understand your question, the syatem works from 2 to 255 nodes. Erik To the best of my knowledge,When a RS485 bus is in idle state,when all nodes are in RX mode,the state of the bus is not clear. And if the bus's A and B lines' potential difference is less than +-200mV, the output state of receivers would be the last bit received. So, inorder to provide an proper idle state at the bus, A line is drawn to GND via an resistance, similarly, B line is drawn to +5V with a resistor of the same value. An over drawn or loose drawn may couse problems. This biasing resistor values depends on the distance and on the number of the nodes that are to be connected to the bus. An adjustment to these resistors is required as any change occurs. My question was if there were any automatic biasing way of the bus you have ever used or known. My second question, switching chips like 4066 or its CMOS versions have substantial switching resistans that changes as with ambient temperature ( typically 25 to 60 ohms) How do you cope with this resistance changes when using this chips during automatic termination. On the other hand, as this chips work as a terminator switcher, they will be exposed to all ESD, unwanted surges, etc.. and are bound to be broken easily and result is a unterminated bus. Thanks in advance |
| Topic | Author | Date |
| RS485 and DE, \RE | 01/01/70 00:00 | |
| not pantyhose | 01/01/70 00:00 | |
| Thanks Erik | 01/01/70 00:00 | |
| stick to the National and B&B stuff | 01/01/70 00:00 | |
| the worse 485 wiring | 01/01/70 00:00 | |
| automatic termination is the solution | 01/01/70 00:00 | |
| what\'s that? | 01/01/70 00:00 | |
| its simple | 01/01/70 00:00 | |
| Cool! | 01/01/70 00:00 | |
| hmmm | 01/01/70 00:00 | |
| actually very simple | 01/01/70 00:00 | |
| I am still none the wiser | 01/01/70 00:00 | |
| chain | 01/01/70 00:00 | |
| I've got it. | 01/01/70 00:00 | |
| It works, you work out the details | 01/01/70 00:00 | |
| maybe not biasing A&B... | 01/01/70 00:00 | |
| then use a high enough voltage | 01/01/70 00:00 | |
| biassing | 01/01/70 00:00 | |
answers | 01/01/70 00:00 | |
| if you supply via cable... | 01/01/70 00:00 | |
| Transceiver with switchable termination | 01/01/70 00:00 | |
| thanks for the tip! | 01/01/70 00:00 | |
| great.Oliver, just this | 01/01/70 00:00 | |
| it would, but think this through | 01/01/70 00:00 |