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[OT, hardware] Combining outputs of MAX3221 and FT232R

 
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kender



Joined: 09 Aug 2004
Posts: 768
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[OT, hardware] Combining outputs of MAX3221 and FT232R
PostPosted: Mon Dec 03, 2007 12:36 am     Reply with quote
Colleagues,

I need to connect the TTL outputs of two RS-232 drivers: MAX3221 and FT232R to one UART on a PIC. Only one transceiver will be transmitting to the PIC at a time. What’s the best way to combine:

* Open collector buffers with wired NOR?
* Gate NOR?

Thanks,
- Nick
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Neutone



Joined: 08 Sep 2003
Posts: 839
Location: Houston

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Re: [OT, hardware] Combining outputs of MAX3221 and FT232R
PostPosted: Mon Dec 03, 2007 12:08 pm     Reply with quote
kender wrote:
Colleagues,

I need to connect the TTL outputs of two RS-232 drivers: MAX3221 and FT232R to one UART on a PIC. Only one transceiver will be transmitting to the PIC at a time. What’s the best way to combine:

* Open collector buffers with wired NOR?
* Gate NOR?

Thanks,
- Nick


The pic RX should be high normally. The TX of both transceivers should be high normally. If one of the transceivers TX goes low the pic RX should go low. This would be AND logic. A pull up resistor on the pic RX with diode pull down from the transceivers will do this. Connect the pic TX to both transceivers RX through resistors. This will allow both transceivers to be used at the same time or just the one that is connected.
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