Post Go back to editing

UART RA issue

Category: Hardware
Product Number: LTC2870

Dear ADI team,

I have a question about LTC2870.

I am seeing a waveform on the receiving RA at the timing to transmit serial communication,
Is this a specification or a malfunction?

I am attaching an image of an oscilloscope.
The top 8 waveforms show the UART and IC pin status of the transmitting and receiving UARTs, as well as the waveforms confirmed with a logic analyzer.
The bottom 4 are RS485 waveforms. RXEN.FEN and LB are all fixed to Low.

S1-UART-TX is the transmit DY waveform. This is converted to RS485 specifications by the IC, output from Y and Z as waveforms of C1 and C2, and received by the receiving IC
S2-UART-RX waveforms are sent to the receiver CPU as S2-UART-RX waveforms.
However, the waveform is output to RA at the timing of transmission (S1-UART-RX).
I would like to confirm if this is the specification.

Also, if I fix DXEN to be valid except when transmitting, this phenomenon will not occur.
This phenomenon does not occur.

Best regards,

  • Hi SYVALION,

    From the above scope picture, the transceiver is in half-duplex mode, H/F\ = high, and the receiver is always on, /RXEN\ = low. Therefore, the receiver always sends out data on the bus, the same data when it is transmitting. You could disable the receiver by setting /RXEN\ to high when the part is transmitting.

    Best,

    Jane