Analysis and reading of CMOS RAM

The cmos ram contains 64-bit real-time clock, and the internal clock circuit uses the first 14 bytes. The rest are used to save the configuration information of other devices. The detailed address allocation of cmos ram is as follows:

Address description
0 seconds
1 second alert
2 points
3-minute alert
4 hours
5-hour alert
6 weeks
7th
August
9 years
A Status Register
B Status Register B
C Status Register C
D Status Register d
E Diagnostic status byte (0 normal)
F stop status byte (0 with mains supply)

10 floppy disk drive type (bit 7-4: A drive, bit 3-0: B Drive 1-360kb; 2-1.2 MB; 6-1.44 MB; 7-720kb)
11 Reserved
12 hard drive type (7-4: C drive, 3-0: D Drive)
13 Reserved
14 device bytes (number of soft drives, display type, coprocessor)
15 low-byte basic memory
16 high-byte basic memory
17 low-byte extended memory
18 extended memory high byte
19 hard disk type bytes (less than 15 is 0)
1a-2d Reserved
2e-2f CMOS checksum (10-2d bytes and)
30 extended memory low byte
31 extended memory high byte
32 century date byte (19 h: 19th century)
33. Information Mark
34-3f reserved (34-0: no password; 35-3f-Password location)

Access to CMOS:

CMOS has two entry addresses: the port address of the address port is 70 h, and the port address of the data port is 71 h. Therefore, you only need to send the address to the address port to read the required data from the 71h.

Read the CMOS Program

Enter the following Assembly statement in debug.

MoV BX, 0

MoV Al, BL

Out 70, Al

In Al, 71

MoV [bx + 130], Al

INC BX

Cmp bx, 40

Jnz start; start is the address of the starting statement mov BX, 0

Then, you can run the debug D command to view the relevant information.