Which parameter in the datasheets of the line drivers MAX3232 and MAX232 can tell about the maximum length of the line for their correct operation if all else is same for the two circuits, that is baud rate = 115200, Vdd = 5 V, same UTP cable used.


100 ohm twisted pair is a poor match for rs232 drivers (which are about 1000 ohms) , the main limitation is the drivers capability to charge and discharge the line.

In my experience on long runs the main problem is dielectric absorbtion during the idle time causing the start bit to be distorted, this can be mitigated somewhat by fitting a diode at the receiver end to limit the negative voltage

So what you want most is low output impedance. voltage levels are less important.

Here the max3232's 35mA short-circuit current beats the max232's 10mA soundly.

  • \$\begingroup\$ If I need to transmit a digital signal that has 50 kHz pulses in it and I want to transmit it to a distance of 100 feet then what type of line driver should I use? \$\endgroup\$ – alt-rose Jul 9 '19 at 9:22
  • \$\begingroup\$ If the required line length is 2 or 3 times longer than what can be handled by a MAX3232 line driver then will it work if I put 2 or 3 extra MAX3232's in the line as repeaters? \$\endgroup\$ – alt-rose Jul 9 '19 at 12:33
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    \$\begingroup\$ use an rs485 driver it takes 2 wires per signal, but works much better on twisted pair, - use an rs485 receiver at the othrer end. you could use etra max 3232s as repeaters, or connect them in parallel at the start of the wire... or get a strong + and - supply and use a pair of emitter followers to boost the output current. \$\endgroup\$ – Jasen Jul 9 '19 at 20:06
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    \$\begingroup\$ I mean those as options, pick one. \$\endgroup\$ – Jasen Jul 9 '19 at 20:12
  • \$\begingroup\$ I only know of the RS232 line drivers MAX3232. Can you tell which is a good RS485 line driver? \$\endgroup\$ – alt-rose Jul 10 '19 at 7:45

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