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Figure 22. The I/O Window

Use the I/O window to manipulate I/O ports.  This is only supported when the
operating system allows application software to use IN and OUT instructions.
 I/O ports can be added to the window, and typed as a byte, word (2 bytes)
or dword (4 bytes).  Use New from the pop-up menu to add a new port to the
window.  Once you have done this, four items will appear on the line.  First
appears the read button which appears as an open book, or [r].  Second
appears the write button.  It is a pencil or [w].  Third appears the port
address, and finally the value.  When you first enter a port address the
value appears as question marks.  The debugger does not automatically read
or write the value since this can have side effects.  In order to read the
displayed value from the port, click on the read button.  To write the
displayed value back, click on the write button.  You can change the value
by double clicking on it, or by cursoring to it and pressing ENTER.  Press
the right mouse button to access the following pop-up menu items:


Modify
    Change the selected item.  You can change either the value field or the
    address field.  This does not write the value back to the port.  You
    must choose Write to write to the port.

New
    Add a new line to the window.  You can have several I/O ports displayed
    at once.

Delete
    Delete the selected line from the window.

Read
    Read the displayed value from the port.

Write
    Write the displayed value to the port.

Type
    Change the display type of the value.  The size of this type determines
    how much is read from or written to the I/O port.