The RTC is addressable via the two registers listed below:
7
6
5
4
3
2
1
0
RTCADD
NMIM
ADDR[6..0]
I/O
RTC Address Register
$070
w
NMIM
NMI Mask. When set, the NMI is disabled.
ADDR[..]
Address selection. This bit field defines the address location within the CMOS
RAM for all consecutive accesses to the RTC Data register RTCDAT.
7
6
5
4
3
2
1
0
RTCDAT
Data[7..0]
I/O
RTC Data Register
$071
DATA[..]
This register allows access to the CMOS RAM at the location previously
defined in the ADDR[..] field of the RTC address register RTCADD.
Note that writing to RTCADD must preserve the status of the NMIM bit in the RTCADD register.
3.2
Keyboard and Mouse Controller
The communication between the PC and the keyboard is managed by a device compatible to the Intel
8042 microcontroller, which also provides the PS/2 mouse interface.
The functions of this device are I/O mapped and communicate with the chip set via two ports:
Adr.
Description
Command
$060
Output buffer
Read
$060
Input buffer
Write
$064
Status register
Read
$064
Command register
Write
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