| ??? 04/30/07 14:24 Read: times |
#138292 - I think it is a lot 'cleaner' to add an inverter Responding to: ???'s previous message |
Due 8051 has "1" as default pin state then during and after reset it happens that RS485 driver output is enabled sending "1". This may disturb other drivers connected to AB line if they do transmit.
To prevent this I use a resistor connected between ground and DE line (its value should be calculated, mine is 1kOhm). Oh, I need say that I use SiLabs chips which have strong "1" output of pins so my suggestion is not usable for "classic" 8051, sorry. Anywhay you should pay attention on this subject. Yes, if you write a '0' to the pin before enabling push-pull it will work. However, I think it is a lot 'cleaner' to add an inverter between the port pin and the transciever, This has the addec advantage that, if using HCT, you get level 3V3 to 5V conversion allowing you to use the 'stronger' 5V 485 transcievers. Erik |
| Topic | Author | Date |
| rs232/rs465 communication | 01/01/70 00:00 | |
| re:rs-232 and rs-485 | 01/01/70 00:00 | |
| rs-232 and rs-485 | 01/01/70 00:00 | |
| with an AND, not if it is properly biased | 01/01/70 00:00 | |
| one more suggestion | 01/01/70 00:00 | |
I think it is a lot 'cleaner' to add an inverter | 01/01/70 00:00 | |
| If it's just for programming... | 01/01/70 00:00 | |
| won't do (in the cases I know of) | 01/01/70 00:00 | |
| NXP | 01/01/70 00:00 | |
| If its for ISP | 01/01/70 00:00 | |
| RS-485 programming | 01/01/70 00:00 |