| ??? 02/04/11 09:54 Read: times |
#180996 - some comments Responding to: ???'s previous message |
Raj Nambiar said: Sometimes it happens :-)
Thanks for the comment. What kind of a hardware did you employ?
Actually hate to parallel MAXs. But no other way. 2. Input of Max has a schmitt. Input impedence is more than 3K. So If my input voltage is around 7 to -7 then the schmitt trip points are well within limits for level sensing. So I am safe there. In single transmitter - single receiver configuration this limits additional resistor value to about 2 k , assuming output impedance is about 1k and voltages , produced by MAX232 (it is 232 right?) are +-7V. 3. Since the output drive of a MAX can drive two MAXs, I am safe there also. Yes, but adding resistors 100..1000 ohm on input wires will be good. MAXes love this kind of protection, even its not specified in datasheet. 4. If both MAXs transmit at the same time, the series resistor should limit the current. Considering that the current would be pulsed and that MAX has built-in current limiting, this part is covered. Here is dangerous part. In case You have two identical tx buffers, powered by identical voltages U+ U-, with identical internal and external current limiting resisors - what will see receiver? I suppose - when one tx emits U+ and other tx emits U-, receiver wil see 0V. - when both emit U+ , receiver will see U+ - when both emit U- , receiver will see U- I suppose You can confirm this,if You check with scope Your setup. Why this still works? Reason is input structure of MAX. But by RS232 specs it is not nececery workable sitution. You can add 2 diodes in parallel to additional resistors - with anode to tx pins. Check with scope difference. Target here is to make pulses with at least +3V (on receiver pin) positive part. 5. If both MAXs transmit at the same time, data would be unusable, and this is the only dangerous part. You really need reliable protocol , or You should change solution, as proposed by others people here. |
| Topic | Author | Date |
| Paralleling Max232 output | 01/01/70 00:00 | |
| Revommedation On Paralleling Outputs | 01/01/70 00:00 | |
| Multiple Mux | 01/01/70 00:00 | |
| Adding another brain is another option. | 01/01/70 00:00 | |
| RS232 is *not* a bus | 01/01/70 00:00 | |
| Two UART | 01/01/70 00:00 | |
| how about a hub | 01/01/70 00:00 | |
| Is there really such a beast? | 01/01/70 00:00 | |
| external UARTs | 01/01/70 00:00 | |
| There once was... | 01/01/70 00:00 | |
| use 422/485 | 01/01/70 00:00 | |
| Can work well but big potentials for trouble | 01/01/70 00:00 | |
| Thanks, Peter.. | 01/01/70 00:00 | |
| I didn't employ anything | 01/01/70 00:00 | |
| some comments | 01/01/70 00:00 | |
| You really need reliable protocol | 01/01/70 00:00 | |
| collision detection | 01/01/70 00:00 | |
Collision avoidance | 01/01/70 00:00 |