E220-900T22D Config request issue

[Robert]

I am using a E220-900T22D with an Arduino Nano Every. I use that particular Nano because it has an extra hardware serial port (Serial1) so I don’t have to use the software serial.
Communication seems to work well including configuring the module with M0 = 1 & M1 = 1.
However, when after configuring I send the configuration request C1 00 08 to get the content of all 8 registers (00H … 07H) back for verification I always receive an extra byte containing NULL (0x00).
Is this a normal behavior? I couldn’t find anything about this additional NULL character in the E220-900T22D manual.

[Renzo Mischianti]

Hi Robert,
I don’t understand the issue, please post your code, and we are going to check It.
Bye Renzo

[Robert]

Hi Renzo,

The problem is that the module seems to send 12 bytes instead of 11 in reply to the request for configuration request. That command comprises 3 bytes : C1 followed by the start address and the number of parameters. For example sending C1 00 08 should result in returning the 3 command bytes followed by the bytes contained in all registers (8 in total : 00H … 07H).
That means 11 bytes in total (i.e. 3 + 8) but it returns 12 bytes, the 12th being 0x00 or the ASCII code for NULL.
The attached screen capture shows the code for reading the returned bytes and displaying them in the serial monitor.

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[Renzo Mischianti]

Hi Robert,
ok, now I understand.
I don’t know why It return 12 bytes, for my library was irrelevant because I use a fixed-size container and I flush the buffer to the end.
Probably It uses that byte like a terminating one.

[Robert]

Hi Renzo,

Thanks for your reply. I will assume it’s a terminating byte (although it’s not mentioned in the data sheet) and I will simply ignore it.

[Author]

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