RS-422/485 Failsafe-Low Receiver (AM26C32, AM26LV32)

Kazu-san,

All devices have no fail safe or fail safe high.

Check out the RS485 design guide here. Put the pull up resistor on 'B' and pull down on 'A' for fail safe low.

http://e2e.ti.com/support/interface/industrial_interface/m/videos__files/264978

Ronald-san,Thank you very much.Best Regards,Kazu Ogawa

Ronald-san,

I have a question.

The customer is going to use Vcc=5V device, so AM26LV32 or DS26LV32AT

These devices have internal failsafe feature.

Can these devices execute the failsafe-low, when put the pull up resistor on 'B' and pull down on 'A' externally, you think?

Best Regards,

Kazu Ogawa

Kazu-san,

Yes, external bias can over power the fail safe internal offset. The internal fail safe has to operate inside the +/-200mV window. External fail safe can provide more than 200mV. However the two systems oppose each other and this lowers the noise immunity.

Ronald-san,Thank you very much.It's not Vcc=5V device but Vcc=3.3V. My mistake.
Best Regards,Kazu Ogawa

Kazu-san,

Rules for 3.3V are same as 5V. Do you know why fail safe low needed (just curious)?

Ronald-san,
I don’t know. The customer said he researched whether there is the possibility of the failsafe-low.
He seems to think it’s an option on the application.Best Regards,Kazu Ogawa