W83977AF Information Storage Devices, Inc, W83977AF Datasheet - Page 128

• Manufacturer Part Number: W83977AF
• Description: W83877TF Plus Kbc, Cir, RTC
• Manufacturer: Information Storage Devices, Inc

9.2
9.2.1 Extended Function Registers
In Compatible PnP, there are two ways to enter Extended Function mode (which is same as
Configure State in Comply PnP) and read or write the configuration registers. HEFRAS (CR26 bit 6)
can be used to select one out of these two methods of entering the Extended Function mode as
follows:
After Power-on reset, the value on RTSA (pin 43) is latched by HEFRAS of CR26. In Compatible
PnP, a specific value (87h) must be written twice to the Extended Functions Enable Register (I/O port
address 3F0h or 370h). Secondly, an index value (02h, 07h-FEh) must be written to the Extended
Functions Index Register (I/O port address 3F0h or 370h same as Extended Functions Enable
Register) to identify which configuration register is to be accessed. The designer can then access the
desired configuration register through the Extended Functions Data Register (I/O port address 3F1h
or 371h).
After programming of the configuration register is finished, an additional value(AAh) should be written
to EFERs to exit the Extended Function mode to prevent unintentional access to those configuration
registers. The designer can also set bit 5 of CR26 (LOCKREG) to high to protect the configuration
registers against accidental accesses.
The configuration registers can be reset to their default or hardware settings only by a cold reset (pin
MR = 1). A warm reset will not affect the configuration registers.
9.2.2 Extended Functions Enable Registers (EFERs)
After a power-on reset, the W83977F/ AF enters the default operating mode. Before the W83977F/
AF enters the extended function mode, a specific value must be programmed into the Extended
Function Enable Register (EFER) so that the extended function register can be accessed. The
Extended Function Enable Registers are write-only registers.
addresses are 3F0h or 370h (as described in previous section).
9.2.3 Extended Function Index Registers (EFIRs), Extended Function Data Registers(EFDRs)
After the extended function mode is entered, the Extended Function Index Register (EFIR) must be
loaded with an index value (02h, 07h-FEh) to access Configuration Register 0 (CR0), Configuration
Register 7 (CR07) to Configuration Register FE (CRFE), and so forth through the Extended Function
Data Register (EFDR).
described in section 12.2.1) on PC/AT systems; the EFDRs are read/write registers with port address
3F1h or 371h (as described in section 9.2.1) on PC/AT systems.
HEFRAS
Compatible PnP
0
1
write 87h to the location 3F0h twice
write 87h to the location 370h twice
The EFIRs are write-only registers with port address 3F0h or 370h (as
address and value
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W83977F/ W83977AF
Publication Release Date: March 1998
On a PC/AT system, their port
PRELIMINARY
Revision 0.58