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Need to combine 2 lines of RS422 to 1 line RS 422
enclosed a file
That's an interesting question. I think if you wanted something that were truly RS-422 compatible at all of the interfaces, the best approach would be the obvious one of using two RS-422 receivers, an OR gate (or equivalent circuit using diodes, etc.), and an RS-422 transmitter.
If there is a lot of margin in the application (i.e., if the distances are short and the signal swing is really 0 V to +5 V as shown in the attachment) and you do not need full standards compliance, then you may be able to get a passive circuit to work. Here is one idea:
This should give a high-level output on C if either A or B are sending a logic high and a low-level output otherwise. It is non-ideal, though, since the diodes will cause some drop in voltage and it is not possible to properly terminate the output. The pull-up and pull-down resistors would need to be much weaker than a typical termination resistance, so if terminated the low-level differential voltage would be closer to 0 V than the desired -5 V.
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In reply to Max Robertson:
Regards,Ronald MichallickLinear Applications
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In reply to Ron Michallick:
In reply to Haim Levy:
The circuit will not need to be very close to system and get better performance using SN75C1167
For the discrete solution simulation, try TI Tina . Use Schottky diode
In reply to Kevin N.:
Thank you Max for the confirmation. Actually, I need to do an RS422 splitter (1 to 2) and RS422 combiner (2 to 1). So there would be 3 devices in the network. I can't figure out how to connect all together. - Splitter: I need to split a signal from device A to device B&C, which is easy considering it is RS422.
- Combiner: I need to combine signals form device B&C to device A. And here is the problem (there can be only one emitter in RS422) The questions are: Can I solve this problem putting a microncontroller+memory between device A and device B&C, so I can combine the frames one after the others? Would it affect the splitter side? Or do I absolutely need to have two separate networks: - One "splitter" network between 3 independant devices (A to B&C)? - One "combiner" network between 3 other independant devices (B'&C' to A')? And what about the termination resistors? My mind is not really clear about it. Thank you for any advices/tips. Kevin.
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