AnsweredAssumed Answered

ADM485 & ADM3485 combination problem

Question asked by bvn123 on May 14, 2015
Latest reply on May 15, 2015 by RAnslow

Hi,

There is properly working kit

  • USB<>RS-485 adapter (CP2102+ADM3485ARZ, terminated by Rt=120 Ohm),
  • short cable
  • PCB (ADM3485ARZ (also Rt=120 Ohm) +ATmega8A under +3.3V PWR)

 

I need to increase the PCB power supply for ATmega8 up to +5V,

but to leave the same adapter with ADM3485ARZ in complect and

WITHOUT ANY CHANGES IN THE SOFTWARE.

 

After replacing <ADM3485ARZ+ATmega8A, U=+3V3> by <ADM485ARZ+ATmega8A, U=+5V>

the failures appear in data exchanges.

 

I read http://www.analog.com/media/en/technical-documentation/application-notes/AN-960.pdf

If my problem may be solved by placing pair of resistors (AN-960.pdf, page 6 'Open Fail-Safe'),

how one should calculate R1 & R2

when

-two PCBs under +5V PWR (ADM485ARZ),

-three PCBs under +3.3V PWR (ADM3485ARZ),

are connected to cable?

 

And are there AD ICs for 3.3V and for 5V, which may be connected to one cable without additional pull-up, pull-down resistors?

 

Best regards,

Vadim

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