When you select "Register" in the popup menu at the top of the Edit Modules dialog box you will see a list of all existing registers. You can edit the parameters associated with any register or create new or delete old registers. The width of a register refers to the number of bits in the register. You cannot edit the contents of the registers (that is, the value stored in the registers) other than their default initial values using this dialog box. To edit a register's contents, use the Register pane that appears on the main desktop.
Parameters:
Initial value: the default value the register will be given whenever the machine is reset or the registers are cleared. The value must be integer that fits in the register in either unsigned integer or 2's complement integer notation. You can specify the integer using base 10, base 2 (using the prefix "0b"), or base 16 (using the prefix "0x").
Read-only: a boolean value indicating whether the register holds a constant and so can only be read rather than read and written.