| ??? 04/15/11 23:13 Read: times |
#181906 - #181903 - AT89c55 Connection with ULN2803/4 Responding to: ???'s previous message |
Actually, the 89c55 is driving a Serial-In_Parallel-Out shift register (74HC595). This chip is driving the ULN.
At startup, the /OE pin of shift register is pulled up, to disable outputs. hence all outputs are Pulled high (TTL state). This causes the relays to turn ON. |
| 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 |