In-Situ Aqua TROLL 400 Modbus and SDI-12 Reference Guide - Manual (Page 61)

Where Byte Count is the #bytes in the Data Payload (does not include CRC bytes).
Byte Count = 2*Register Count.
The register count is limited to a single data format field. If an attempt is made to write a data
field with an incorrect register count, the device will return a Modbus exception response with
error code 0x80.
8.10.4 Mask Write Register
This command will set and/or clear one or more bits in a single register.
Message : Response:
Address 1 Byte 1-247 Address 1 Byte 1-247
Function Code 1 Byte 0x16 Function Code 1 Byte 0x16
Data Address 2 Bytes 0 to 0xFFFF Data Address 2 Bytes 0 to 0xFFFF
And_Mask 2 Bytes 0 to 0xFFFF And_Mask 2 Bytes 0 to 0xFFFF
Or_Mask 2 Bytes 0 to 0xFFFF Or_Mask 2 Bytes 0 to 0xFFFF
CRC 2 Bytes CRC 2 Bytes
Register = (Register Value AND And_Mask) OR (Or_Mask AND (NOT And_Mask))
And_Mask: 0 = bits to change, 1 = bits to leave unchanged.
Or_Mask: 0 = bits to clear, 1 = bits to set.
Example: - set bit 1 (LSB), clear bit 2, leave remaining bits unchanged
Old Value: 0x007E 0000 0000 0111 1110
And_Mask: 0xFFFC 1111 1111 1111 1100
Or_Mask: 0x0001 0000 0000 0000 0001
New Value: 0x007D 0000 0000 0111 1101
This command is useful in a bit mapped register where the Master wants to set some bits of a
register that are mapped to a feature without disturbing the other bits of the register that might
be mapped to a different feature.
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