AMD SB600 Technical Reference Manual page 295

Extended RAM Address Port - RW – 8 bits - [RTC_Reg: 50h]
Field Name
ExtendedRAMAddr
Reserved
Extended RAM Address Port register: The address port to access Extended RAM.
Extended RAM Data Port - RW – 8 bits - [RTC_Reg: 53h]
Field Name
Extended RAM Data Port
Extended RAM Data Port register.
Field Name
RtcTimeClear
Reserved
RTC Time Clear register.
Field Name
RtcRamEnable
Reserved
RTC RAM Enable register.
©2008 Advanced Micro Devices, Inc.
AMD SB600 Register Reference Manual
Bits Default
6:0 00h
7
Bits Default
7:0 xxxxxxxx
RTC Time Clear - RW – 8 bits - [RTC_Reg: 7Eh]
Bits Default
0 0b
7:1 0000000b
RTC RAM Enable - RW – 8 bits - [RTC_Reg: 7Fh]
Bits Default
0 1b
7:1 0000000b
Description
Because only 7 address bits are used in port x70, only
lower 128 bytes are accessible through port x71. The
Extended RAM (upper 128 bytes) are physically located
at address 80H to FFH. In order to access these
address, an address offset should be programmed into
this register and access them through Extended
RAMDataPort. (An offset of x80H will automatically add
to this 7-bit address).
Description
There is no physical register corresponding to this data
port but the data port address is used for decoding to
generate appropriate internal control signals.
Description
Setting this bit will clear the RTC second and RTC time
will stop
Description
Setting this bit will enable access to the RTC RAM
Proprietary
Real Time Clock (RTC)
Page 295