| ??? 04/16/11 01:17 Read: times |
#181907 - '595 Chip /OE Responding to: ???'s previous message |
The initial pulled up /OE will tristate the shift register outputs.
Secondly when the /OE is eventually pulled low the '595 is able to drive to the ULN part with a push-pull driver and can easily put the ULN input to high orlow level. So instead of having pullups on the outputs of the '595 why don't you instead provide forpull-down resistors which would force the ULN off whenever the '595 is tristated. The pull-down , if kept to a reasonable resistance should not represent a problem for the active outputs of the '595 when it has to source current to turn on the ULN. Simple electronics this issue. Michael Karas |
| Topic | Author | Date |
| AT89c55 Connection with ULN2803/4 | 01/01/70 00:00 | |
| There is a FAQ for that | 01/01/70 00:00 | |
| MAX1232 + some NORs | 01/01/70 00:00 | |
| #181903 - AT89c55 Connection with ULN2803/4 | 01/01/70 00:00 | |
| '595 Chip /OE | 01/01/70 00:00 | |
| Pull-downs... | 01/01/70 00:00 | |
| 89C55 connection with 2803 | 01/01/70 00:00 | |
| Why? | 01/01/70 00:00 | |
| Why is Atmel different? | 01/01/70 00:00 | |
| Why 89CXX is different | 01/01/70 00:00 | |
| Advice not understood | 01/01/70 00:00 | |
| You didn't answer the question! | 01/01/70 00:00 | |
| Answer | 01/01/70 00:00 | |
not necessarily because of AT89 | 01/01/70 00:00 |