THVD4411: 5k Termination Resistor for RS232

JLinzm

Part Number: THVD4411

Tool/software:

Hi,

I want to connect the RS232 and RS485 lines for a selectable protocol on the same pins. Is the 5k termination resistor disconnected from the lines when RS485 is selected as MODE? Is there another way of disabling the 5k resistor just like the 120R termination for RS485?

Best Regards

Jan

8 months ago

0 JLinzm 8 months ago

Prodigy 20 points

The original questiuon is not the right one, I wanted to link this one : https://e2e.ti.com/support/interface-group/interface/f/interface-forum/1386133/thvd4411-shared-rs232-rs485-pinout

0 JLinzm 8 months ago

Prodigy 20 points

Also what happens if the device is diabled when SHDN is LOW? Is R2 High Impedance or is there still 5k to ground? Because if many of these Chips get used in multidrop rs485 Mode this 5k pulldown would lead to an samller and smaller resistance on the Bus.

+1 Parker Dodson 8 months ago

TI__Guru 52432 points

Hi Jan,

The 5k pull-down resistance only applies in RS-232 mode - it is not present in RS-485 mode.

5k is only there in RS-232 mode as shown above.

No you cannot disable the 5k pull-down when in RS-232 mode while /SHDN = VIO; it is required by RS-232 standard that the receiver typically has a 5k resistor (minimum 3k) - this resistor is required for RS-232 compliance.

If the device is in RS-232 mode when the /SHDN pin is pulled to GND the receiver goes high impedance:

Please let me know if you have any other questions and I will see what I can do.

Best,

Parker Dodson

Interface

Interface forum

THVD4411: 5k Termination Resistor for RS232