| ??? 03/10/07 22:11 Modified: 03/10/07 22:14 Read: times |
#134688 - you will most likely need pullups Responding to: ???'s previous message |
What happens to the signals on your parallel cable when you unplug it? It becomes an antenna. Since the input impedance of your cmos logic is high - the input signals will dance around randomly. So you need some pullup (or pulldown) resistors - say around 4.7k. Why did you not use LS TTL? - you may have avoided the problem!
There's a long history as to why most signals are active low - thus the use of pullups. Mike - you're getting closer to the way we originally suggested. Pity you didn't build your hardware rom - you just avoided a big exercise in futility. |
| Topic | Author | Date |
| 8051 board somewhat working | 01/01/70 00:00 | |
| Give us a clue then.How does it partialy work?? | 01/01/70 00:00 | |
| HC AC ???? | 01/01/70 00:00 | |
| you will most likely need pullups | 01/01/70 00:00 | |
| pull ups | 01/01/70 00:00 | |
| be more specific | 01/01/70 00:00 | |
| interesting tests | 01/01/70 00:00 | |
| interesting they may be, but | 01/01/70 00:00 | |
| to verify | 01/01/70 00:00 | |
| interesting they may be, | 01/01/70 00:00 | |
| Checksum? CRC? | 01/01/70 00:00 | |
| hmm | 01/01/70 00:00 | |
| You probably need an oscilloscope | 01/01/70 00:00 | |
| sorry for asking | 01/01/70 00:00 | |
| not the first... (or last :-) | 01/01/70 00:00 | |
| Maybe my naging helped ... | 01/01/70 00:00 | |
| why EPP? | 01/01/70 00:00 | |
| why epp can be faster | 01/01/70 00:00 | |
| Epp requires a bit less logic and is WAY faster | 01/01/70 00:00 | |
| about that schematic ... | 01/01/70 00:00 | |
| a matter of taste | 01/01/70 00:00 | |
| I have to agree ... | 01/01/70 00:00 | |
you may not have discovered this | 01/01/70 00:00 | |
| you have to investigate | 01/01/70 00:00 | |
| indeed | 01/01/70 00:00 | |
| Amazed! | 01/01/70 00:00 | |
| What? | 01/01/70 00:00 |