| ??? 01/21/05 14:04 Read: times |
#85500 - Misleading.... Responding to: ???'s previous message |
Erik:
Your reply to "NEVER pull an input pin high, only pull it low" is a misleading statement and may actually confuse many readers here. Case on fact is that it is highly desireable to use resistors on 8051 type input pins to pull them to high levels when the line is in its idle state. In this case then the circuit that connects to the input can drive the signal to a low level by overcoming the pullup resistor. I think what you may have actually been trying to state in your post was that ... "NEVER drive an input pin high, only drive it low". A better approach would be to say that the use of pull-down resistors should be discouraged in favor of using pullup resistors. Michael Karas |
| Topic | Author | Date |
| Inputs | 01/01/70 00:00 | |
| Opto | 01/01/70 00:00 | |
| Opto input | 01/01/70 00:00 | |
| Optocoupler Designer’s Guide | 01/01/70 00:00 | |
| What type of opto? | 01/01/70 00:00 | |
| pulling high | 01/01/70 00:00 | |
| Why??? | 01/01/70 00:00 | |
| Misleading.... | 01/01/70 00:00 | |
| OK, clearer | 01/01/70 00:00 | |
| I must be stupid... | 01/01/70 00:00 | |
| you are not | 01/01/70 00:00 | |
| Heres Why | 01/01/70 00:00 | |
| Not quite so. | 01/01/70 00:00 | |
| Pull-downs must be much smaller! | 01/01/70 00:00 | |
| OK you are right. | 01/01/70 00:00 | |
A little history | 01/01/70 00:00 | |
| Link... | 01/01/70 00:00 | |
| use opto-coupler as NPN | 01/01/70 00:00 | |
| Thank you All, & a question for Kai | 01/01/70 00:00 | |
| Opto to pull-down signal | 01/01/70 00:00 |