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There are three steps to complete the configuration setup: (1) Enter the MB PnP Mode;
(2) Modify the data of configuration registers; (3) Exit the MB PnP Mode. Undesired
result may occur if the MB PnP Mode is not exited normally.
(1) Enter the MB PnP Mode
To enter the MB PnP Mode, four special I/O write operations are to be performed
during Wait for Key state. To ensure the initial state of the key-check logic, it is
necessary to perform four write operations to the Special Address port (2EH). Two
different enter keys are provided to select configuration ports (2Eh/2Fh) of the next
step.
(2) Modify the Data of the Registers
All configuration registers can be accessed after entering the MB PnP Mode. Before
accessing a selected register, the content of Index 07h must be changed to the LDN to
which the register belongs, except some Global registers.
(3) Exit the MB PnP Mode
Write exit key 0xAA to the index port.
Appendix A – Watchdog Timer Programming
107
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