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Topic: Serial Question -- TTL for RX and RS232 for TX (Read 12631 times) previous topic - next topic


Sep 22, 2010, 04:22 am Last Edit: Sep 22, 2010, 04:24 am by Mavromatis Reason: 1
Well... took a device apart... looks like they are using a MAX3082 (RS422) driver... no clue why it's working.  guess because it has failsafes (http://www.maxim-ic.com/datasheet/index.mvp/id/1522)

Also, the MAX3082/MAX3085/MAX3088 are intended for halfduplex communications....

These devices feature fail-safe circuitry, which guarantees a logic-high receiver output when the receiver inputs are open or shorted. This means that the receiver output will be a logic high if all transmitters on a terminated bus are disabled (high impedance).


Still unclear why it works using TTL and RS232 but I'll stick with RS422 to keep things "in spec".


Agree.  Just ordered some more parts... I'll report back how it turns out.   Thanks again!




I have got a USB to Serial (TTL)  module, Can I use this TTL module to write and read from Arduino Board in serial mode ?

Thanks in advance for your help.


Jan 21, 2011, 10:51 am Last Edit: Jan 21, 2011, 11:03 am by retrolefty Reason: 1
But Half-duplex went out of style with the old mechanical telegraph before any of us were born.

Half-duplex communications links lived well past the mechanical telegraph age, on to the magic age of electro-mechanical teletype machines, then on to the wonderful world of time-shared computing.

I worked on many half-duplex serial loops using both 20ma and 60ma current loop and RS-232 voltage levels, up until the mid 70s.

In that era if you needed to have a cost effective communications link between two nodes too far to run your own cable, or off your property, you leased a private datalink from the phone company or possibly western union. Cost for a single wire pair link was less then for a two wire pair (go figure!) so if cost were a factor, you would lease the single pair and run the modems in half duplex mode.

110 to 1200 baud were common speeds, but with higher cost 'equalized' lines (cost more!) one could make it up to 9600 baud with proper modems. Which by the way in the early 70s, a 9600 baud modem, if purchased would set your back around $10,000+ (adjust that to today's dollars!), and it was the size of desk top PC laid on it's side, usually rack mounted.

And even back then we were converting current loop and RS-232 links to and from TTL voltage levels, some things don't change!

[edit]What cost $10000 in 1970 would cost $54639.18 in 2009.[/edit]

Yes, I'm old, and yes my lawn is off limits.

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