| ??? 08/06/09 15:27 Modified: 08/06/09 15:29 Read: times |
#168225 - 6N138 can be strobed at Vb pin... Responding to: ???'s previous message |
You could use a free port0 pin of micro (open drain output) to pull the Vb pin of 6N138 to GND and by this turning off the opto. The SN75176 has the /RE input to turn this chip off and could be connected to another free port pin to accomplish this.
So, you could connect a pull-up of 2k2 from Vcc to the output of opto, connect this output to the output of SN75176 via 330R resistor and connect the output of SN75176 via a 330R resistor to the RXD input of micro. Do also use a 330R resistor in the connection from Vb pin of opto to the micro's port0 pin. The 330R resistors are useful to limit unwanted inrush currents during power-on reset as long as the micro isn't properly resetted and the involved chips can emit undefined levels. With a poor crystal and a synchronous reset this undesired period can last rather long and cause damage. Use a resistor array for the three 330R resistors to save board area. Kai |
| Topic | Author | Date |
| Digitally switching RX input | 01/01/70 00:00 | |
| Multiplexing | 01/01/70 00:00 | |
| tristate | 01/01/70 00:00 | |
| Spare chips | 01/01/70 00:00 | |
| You can build a 2:1 mux | 01/01/70 00:00 | |
| I vote for Richard's method | 01/01/70 00:00 | |
| 6N138 can be strobed at Vb pin... | 01/01/70 00:00 | |
| Have you considered a chip with 2 UARTs? | 01/01/70 00:00 | |
two diodes and a resistor | 01/01/70 00:00 |