| ??? 12/27/12 20:35 Modified: 12/27/12 20:42 Read: times |
#189049 - Found it Responding to: ???'s previous message |
As Kai pointed out above:
In ten ways to bulletproof RS485 http://www.ti.com/lit/an/snla049a/snla049a.pdf 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!. Mahmood |
| Topic | Author | Date |
| RS485 supply voltage | 01/01/70 00:00 | |
| Could the data rate be a problem? | 01/01/70 00:00 | |
| 5V | 01/01/70 00:00 | |
| No! | 01/01/70 00:00 | |
| Strange! | 01/01/70 00:00 | |
| stubs? | 01/01/70 00:00 | |
| Found it | 01/01/70 00:00 | |
| I made $$ on that one | 01/01/70 00:00 | |
| How to Protect ? | 01/01/70 00:00 | |
| Use MAX3430 | 01/01/70 00:00 | |
| Or the LT1785... | 01/01/70 00:00 | |
| MAX485 | 01/01/70 00:00 | |
low | 01/01/70 00:00 |