Siglent 1202X – serial decoder issues

[klostery]

Siglent 1202X – serial decoder issues or firmware bug ?

Verifying the initial communication of an energy meter I end up to debug the serial UART decoder of my scope (Siglent 1202X-E – Hardware 00-02 – Software 1.3.26).

The scope is connected to TX line (yellow trace) and RX line (pink trace) of the serial communication from a master (ATtiny84) to an energy meter (CS5490). After reset the energy meter starts with 600 baud, 1 start bit, 8 data bits, 1 stop bit, idle = high level.

The first screenshot shows one errors of the decoder:

• To select the register page the master sends the command 0x80. The decoder of the scope outputs a value 0x00 as decoded data. That is not correct. This is an error.
  The yellow trace shows between the markers the start bit (0) and the 8 data bits 0b1000000 = 0x80. Timing is o.k. – t = 600 baud x 9 bit = 15 ms. Stop bit is outside the cursors so that the MSB is the last bit (logical 1) inside the cursors.
  

The second screenshot shows another error of the decoder:

• To read the config register the master sends the command 0x00. The decoder of the scope outputs a data error. That is not correct. This is an error.
  The yellow trace shows between the markers the start bit (0) and the 8 data bits 0b0000000 = 0x00. Timing is o.k. – t = 600 baud x 9 bit = 15 ms. Stop bit is outside the cursors so that the MSB is the last bit (logical 0) inside the cursors.
  By the way, the reply of the energy meter is 0x00, 0x20, 0xC0 and correct decoded.
  

The third screenshot shows the complete start of the communication. It contains both errors.



After that I checked some other byte values to be decoded:
-   Correct decoded bytes: 0x01, 0x7F, 0x81, 0x55, 0xAA, 0xFF.
-   Faulty decoded bytes: 0x00, 0x80.

These errors are independent of the baud rate. Using 9600 baud the pictures are nearly the same only the timescale is different.

May someone doublecheck my observations with another Siglent 1202X or Siglent xxxx?

How to fix the UART decoder problem?
-   To change the protocol of the energy meter is not an option.
-   Should the scope be returned?
-   Is a firmware update planed or available on request?