w83977tf Winbond Electronics Corp America, w83977tf Datasheet - Page 86

• Manufacturer Part Number: w83977tf
• Description: Winbond I/o
• Manufacturer: Winbond Electronics Corp America

W83977TF
PRELIMINARY
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-FFh) 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.
8.1.2 Extended Functions Enable Registers (EFERs)
After a power-on reset, the
W83977TF
enters the default operating mode. Before the
W83977TF
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. On a PC/AT system, their port addresses are
3F0h or 370h (as described in previous section).
8.1.3 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).
The EFIRs are write-only registers with port address 3F0h or 370h (as
described in section 8.1.1) on PC/AT systems; the EFDRs are read/write registers with port address
3F1h or 371h (as described in section 8.1.1) on PC/AT systems.
Publication Release Date:March 1998
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Revision 0.62