For Analog point types in Input/Output memory types, only addresses that fall on byte boundaries are valid for analog points. To verify that the address is valid, use the following formula:
check = (address - 1) mod 8
where address is the number of one of the starting bit in the memory type that you want to use for the Analog point address. If check is zero (0), the address is valid. Otherwise, the address is invalid.
For example, an address of I18 is not valid because:
check = (18 - 1) mod 8 = 17 mod 8 = 1
An address of I25 is valid because:
check = (25 - 1) mod 8 = 24 mod 8 = 0
Input/output memory addressing.