UART Multiplexing
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From: Greegor on 11 Apr 2010 05:49 "eeboy", Are you just a shill trying to "seed" your web page hookup to this usenet thread? You want to apply LOTS of engineering time because a $2.70 part is too expensive for your one-off project? What you're describing is an electronic version of an A/B switch, correct? Why wouldn't 9600 Baud do the job? If you're using 115K Baud will you be using all of the SECONDARY RS232 pins/lines as well? http://en.wikipedia.org/wiki/RS-232#Secondary_channel
From: D Yuniskis on 11 Apr 2010 13:06 Greegor wrote: > You want to apply LOTS of engineering time > because a $2.70 part is too expensive for > your one-off project? Hmmm... I see nothing in his post to indicate this is "one off". > What you're describing is an electronic version > of an A/B switch, correct? That's how I have read it. In which case, all of the steering logic can be done on the "low voltage" side as I've indicated in another post (gate the unused TxD to Marking while simultaneously inhibiting input from the deselected RxD). > Why wouldn't 9600 Baud do the job? Shouldn't matter -- except on the translated ("hi voltage") side. There, it usually places limits on cable length. > If you're using 115K Baud will you be > using all of the SECONDARY RS232 > pins/lines as well? > > http://en.wikipedia.org/wiki/RS-232#Secondary_channel I've seen scant few products actually use any of these pins. The last that I was involved with only cherry picked some pins (mainly offering alternatives to their counterparts in the primary channel -- e.g., I recall a configuration option in one product that allowed SRTS to be used in lieu of RTS... compatibility with some archaic bit of kit). One product tried to economize on connector shells by routing it's two serial ports to a single DB25. This went over like a lead balloon -- *everyone* needed an adapter cable to split those two channels back out into their intended separate channels (i.e., cost of the external Y cable vastly exceeded the savings of one less connector shell in the product!). Also, the secondary channel doesn't (IIRC) support the full complement of signals. Nowadays, you could squeak by without the "extras" (in most cases) as few other devices need/want those signals (OTOH, back in the 70's, RS232 was still much more rigidly implemented -- e.g., the role of the "handshaking" signals has changed over the years from that which was originally laid out)
From: eeboy on 11 Apr 2010 18:35 >You want to apply LOTS of engineering time >because a $2.70 part is too expensive for >your one-off project? > This isn't a one off. >What you're describing is an electronic version >of an A/B switch, correct? > Correct. >Why wouldn't 9600 Baud do the job? > Because it doesn't fit the application. >If you're using 115K Baud will you be >using all of the SECONDARY RS232 >pins/lines as well? > >http://en.wikipedia.org/wiki/RS-232#Secondary_channel > One thing I may not have been clear on. The communications from the UART peripheral of the micro is simply logic level asynchronous serial consisting of an RX and TX signal. No handshaking, no RS-232 voltage levels. --------------------------------------- Posted through http://www.Electronics-Related.com
From: eeboy on 11 Apr 2010 18:40 > >Sounds quite desperate trying to multiplex the UART. > Perhaps. I've got 3 UART peripherals on my micro and 4 UART enabled devices. The 4th device is a new addition, so I am having to retrofit the board. I could implement a software UART, choose another micro with 4 UART peripherals, or multiplex one UART. The last made the most sense to me since this newest device can only operate when the other device is not. >Are the devices addressable ? If so, an open collector (wired-OR) bus >with 5 V tolerant devices should do the trick. > Unfortunately no. --------------------------------------- Posted through http://www.Electronics-Related.com
From: eeboy on 11 Apr 2010 18:44
> >74HC4051 > Sounds like the best solution so far... just don't like that I have to use two (RX and TX) of these large (relative) components. --------------------------------------- Posted through http://www.Electronics-Related.com |