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[SOLVED] Do I need resistors for Intersi's HIN232 (MAX232 alternative)?

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elPresidente

elPresidente

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Sorry for such a newbie question but i can't figure it out myself. I use four RS232 lines, RX, TX, DTR and DSR. My PIC uC has 2 of them implemented in hardware - RX and TX but DTR and DSR i have to use with normal GPIO ports. I was alway connecting outputs from MAX232 (now HIN232 ) directly to uC without any current limiting resistors but now i'm hesitating if it is a good way to do.
In datasheet of HIN232 https://www.intersil.com/content/dam/Intersil/documents/fn31/fn3138.pdf it is written that receivers have from 3k to 7k input impedance, ok but what about output impedance, do i need there resistors? And what about transmiters which have > 300ohms output impedance?

Do i need those resistors or it's not required, or maybe even not recommended?
 

No, you don't need them. The data sheet is referring to the impedances built-in to the IC which are already optimized for RS232 lines. They are specified in case of unusual conditions where more than one transmitter or reciver is connected to a single wire and it's necessary to consider their loading effects and drive capability. For normal use, just connect the communication wires directly to the IC.

Brian.
 
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