Language learning Notes (14) port

The CPU can read data from three locations directly
1) Internal CPU registers
2) Memory
3) port

Port (referred to as hardware port 8086) Read and write two instructions: in and out
Access memory: mov ax,ds:[8]
Access port: in al,60h; reads a byte from the 60h port (0-65535)

In and out instructions, you can only use Ax or Al to hold the port's data

CMOS RAM chip: RAM memory containing a real-time clock and a 128 storage unit
0~DH storage time, rest storage System Information
70H: Address port, storing the address of the Cmosram unit to be accessed;
71H: A data port that holds data read from a selected Cmosram unit or data to which it is written


SHL: Logical Left SHIFT (* *): The last move out of a write CF, the lowest bit with 0 supplement
MOV al,01010001b
MOV cl,3
SHL Al,cl (move left 3-bit)
This is the value of CF: 0

SHR: Logical Right Shift (/2): The last-removed one is written to CF, the highest bit is supplemented with 0

Time information stored in RAM:
BCD Code
+30H can be converted directly to 10 binary