Since the Dev Address field is a signed 16-bit integer, the maximum positive value accepted by RSLogix is 32767
However the Dev Address field is a Modbus offset value. When using a Modbus function code 3, 6, or 16, an address base of 40001 is assumed. The Dev Address field is an offset from this base.
Examples:
If the required OFFSET actually exceeds 32767, add 65536 to calculate the signed value of this address, and that value will be accepted as a signed 16 bit INT.