Real values in AVEVA communication Modbus

I'm a bit confused from your second example: do you have a REAL variable definition with address %MW39 as well as %MW38?
REALs take up two consecutive modbus registers, so a REAL at %MW39 should not exist if you already have a REAL at %MW38.

I'm not too familiar with M221 PLCs, but with modbus devices in general you first have determine whether you have
a) a register shift problem (0-based addressing vs. 1-based addressing)
b) a byte order problem
or both...

To determine if you have a register shift issue, you should define an INT variable on both sides at equal address, and test with small and large values (say 1 and 10000). If writing to these variables from SCADA results in value changes in other addresses (N + 1 or N - 1) in the PLC then you have to switch to a MODNET variant with a different base address, in your case from MODNET30 to MODNET20.

If your INT variables work fine, but your REAL and/or LONG values are garbled, then you have a byte-order problem, which you can fix using [MODNET] parameters. For REALs you can use [MODNET]FloatMode (as Jacky mentioned) and for LONGs you can adjust [MODNET]LongDataType.

Please pay attention to Jacky's note however: both parameters mentioned here cannot be used for MODNET30 and MODNET20 protocol variants. You will have to switch to a standard MODNET, MODNET1, MODNET2, or MODNET3 variant in this case, and you have to change your variable address notation as well because these standard variants do not support %MW notation (change %MW38 to 400038 in your example).

I'm a bit confused from your second example: do you have a REAL variable definition with address %MW39 as well as %MW38?
REALs take up two consecutive modbus registers, so a REAL at %MW39 should not exist if you already have a REAL at %MW38.

I'm not too familiar with M221 PLCs, but with modbus devices in general you first have determine whether you have
a) a register shift problem (0-based addressing vs. 1-based addressing)
b) a byte order problem
or both...

To determine if you have a register shift issue, you should define an INT variable on both sides at equal address, and test with small and large values (say 1 and 10000). If writing to these variables from SCADA results in value changes in other addresses (N + 1 or N - 1) in the PLC then you have to switch to a MODNET variant with a different base address, in your case from MODNET30 to MODNET20.

If your INT variables work fine, but your REAL and/or LONG values are garbled, then you have a byte-order problem, which you can fix using [MODNET] parameters. For REALs you can use [MODNET]FloatMode (as Jacky mentioned) and for LONGs you can adjust [MODNET]LongDataType.

Please pay attention to Jacky's note however: both parameters mentioned here cannot be used for MODNET30 and MODNET20 protocol variants. You will have to switch to a standard MODNET, MODNET1, MODNET2, or MODNET3 variant in this case, and you have to change your variable address notation as well because these standard variants do not support %MW notation (change %MW38 to 400038 in your example).