| ??? 02/19/09 17:43 Read: times |
#162573 - The 120 ohm resistor Responding to: ???'s previous message |
Did you put the resistor across between the (A) and (B) wires of the bus?
You should check with a scope as to what is happening with the signal level when you insert and remove the resistor. Maybe you have a problem of not having an adequate VCC and GND return to the driver chip in the master and the signal level is suffering greatly when you add the 120 ohm load to the bus. You didn't mention if you are trying to operate with a local VCC of 3.3V or 5V. All the RS485 setups I've worked with have been 5V setups. Maybe in your case you are trying to use 3.3V and the driver is not able to work correctly under load at 3.3V. Michael Karas |
| Topic | Author | Date |
| RS485 problem | 01/01/70 00:00 | |
| Just 1? | 01/01/70 00:00 | |
| The 120 ohm resistor | 01/01/70 00:00 | |
| VCC = 5V | 01/01/70 00:00 | |
| you need | 01/01/70 00:00 | |
| Scope? | 01/01/70 00:00 | |
| daisy chain | 01/01/70 00:00 | |
| Some hints... | 01/01/70 00:00 | |
| 100 meters | 01/01/70 00:00 | |
| 7 clocks | 01/01/70 00:00 | |
| Topology | 01/01/70 00:00 | |
| RE: topology | 01/01/70 00:00 | |
| don't | 01/01/70 00:00 | |
| Yes, don't! | 01/01/70 00:00 | |
| Getting there | 01/01/70 00:00 | |
| So, what was the cause of failure? | 01/01/70 00:00 | |
| not yet | 01/01/70 00:00 | |
| with additional components | 01/01/70 00:00 | |
| Where do you have this circuit from? | 01/01/70 00:00 | |
| from my Mentor | 01/01/70 00:00 | |
| Ben's site | 01/01/70 00:00 | |
| Mission Accomplished | 01/01/70 00:00 | |
| I'm not sure I agree | 01/01/70 00:00 | |
| exactly | 01/01/70 00:00 | |
| Maybe I misunderstood your earlier post | 01/01/70 00:00 | |
no | 01/01/70 00:00 | |
| yes | 01/01/70 00:00 | |
| then how could you ask .. | 01/01/70 00:00 | |
| With noise+etc reduction | 01/01/70 00:00 | |
| email updated | 01/01/70 00:00 | |
| here's info's........ | 01/01/70 00:00 | |
| That means you get | 01/01/70 00:00 | |
| Only when seeing nosie? | 01/01/70 00:00 | |
| Not exactly but as per requirement | 01/01/70 00:00 | |
| CAT5 ethernet cable | 01/01/70 00:00 | |
| 100 Ohm | 01/01/70 00:00 | |
| More details here | 01/01/70 00:00 | |
| did you check the FAQ? | 01/01/70 00:00 |