Echo Effect

Hi Colbee,

I cannot see the complete threads of the two previous posts. The MAX13487E is an AutoDirection Control RS485 transceiver, which allows the AutoDirection circuit to control the receiver with RE = H. The Function Tables on page 11 shows RO is at H-Z (receiver is off) only during AutoDirecion circuit controlling the receiver with SHDN = 1, RE =1, and driver is on. The receiver is on when the driver is off during AutoDirction control with RE = 1.

Best,

Jane

Hi, I'm sorry you cannot see the prior discusison - the question from within your Q&A  section was as follows

what is the reason behind getting "Echo" at the RO pin for the part MAX13487E?
When the RE pin is pulled up, the data received at the DI pin can be seen at the RO pin. But actually it is not echo.

when there is a High at DI pin then the driver is OFF and the receiver is ON , as the VAB>=200mV, the RO will be HIgh.

When the DI is low, the Driver is ON and VAB <=200mV, so the RO will be Low. This effect is perceived as the Echo, but actually its not.

And in a second question

How to avoid the Echo effect for the MAX13487E ?
Connecting a pull up resistor to RE pin will avoid echo effect in MAX13487E and MAX13488E

So my question is, which one actually solve the echo issue ? It seems it's cause it having RE high, which as i understand enable auto direction, but the latter reply, suggests it can be solved by also pulling RE high ?

Thankyou

Hi Colbee,

Typically, a half-duplex RS485 transceiver includes /RE pin for options turn on or off the receiver, and the receiver is off when /RE = H.  Since MAX13487 is in AutoDirection Control mode when /RE =H, the receiver can be only turned off through AutoDirection with driver is on. Both answers provided you the solution is pulling /RE pin to high (/RE=H, or connecting a pull up resistor), which is correct. The first answer just explained in more detail how the part will turn off the receiver.

Best,

Jane