
4-2
Configuration Registers
4.1
CONFIGURATION REGISTER OVERVIEW
There are two basic types of registers that are used to configure the élanSC310 micro-
controller:
I
Port registers
I
Index registers
4.1.1
Port Registers
The configuration port registers are located in I/O space. They are addressed directly by
the élanSC310 microcontroller. The configuration port registers are listed in Table 4-1 on
page 4-2. For a description of each port register, see “Configuration Port Registers” on
page 4-11.
The Configuration Address register points to the index register to be read or written when
a data-register I/O cycle occurs. The Configuration Data register is used to read or write
the index register.
Reading the Configuration Data register reads the contents of the index register. Writing a
value to the Configuration Data register writes that value to the index register.
The contents of the Configuration Address register is static relative to multiple data regis-
ter reads and writes. This allows for read-modify-write operations. The address of the
index register is written to the Configuration Address register, and then the data is read,
modified, and written back to the Configuration Data register without rewriting the Config-
uration Address register.
4.1.2
Index Registers
The configuration index registers are located in a separate internal memory space. They
are addressed indirectly by the élanSC310 microcontroller. For a description of each
index register, see “Configuration Index Registers” on page 4-11.
4.1.2.1
Mandatory Settings
Default settings of the microcontroller guarantee that code can be fetched and executed
out of the ROM BIOS address space and that the configuration index registers can be
accessed upon power up. Several of the configuration index registers contain bits that
must be written soon after reset with their specified values in order for the device to oper-
ate as specified. These mandatory bits control things such as chip-test modes, interrupt
mapping, SMI generation, and cycle timings.
Table 4-1
Configuration Port Registers
Port
Register
022h
Configuration Address
023h
Configuration Data