Modbus Exception 0x04

  • Thread starter syefano sormanni
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syefano sormanni

Hi All,

I'm reading from a Modbus slave some address from a Shore power converter (SCP). The master is a Schneider Electric Combo (PLC+OP). When I'm connecting the first time the modbus cable (both system are powered on) I receive the code error 04H and I don't understand the real reason of this error.

The writing area is from 0x00 to 0x10, and reading area is from 0x1000 to 0x1100. I simulate with a modbus slave software the whore area from 0x00 to 0x1100, and no error appeared. The explanation of the error is "slave not ready" but I don't recognize the reason of this error.

has someone met this problem?

Thanks a lot

Lynn August Linse

You'll need to ask the vendor, as such exceptions are variously defined & so 100% vendor-specific. I would guess that perhaps the meter is still trying to sync itself to the AC sin-wave so it can read the peaks, etc. As long as future polls work, you'll just have to treat this as a no-response.

Unfortunately, some master tools treat an unknown error as very bad - like configuration errors. As has been said many times on this forum, this is the problem with device vendors trying to be too creative with Modbus exceptions; few master tools bother trying to make intelligent use of exception responses.
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