Analysis of the soft test: the morning test paper in the first half of 2016

2.【Basic knowledge of computer system】

3.【Basic knowledge of computer system】

Knowledge points:

Knowing an original code, there are two cases for the operation of obtaining the complement code:
(1) The complement code of a positive number: the same as the original code.
      For example, +9's complement is 00001001.
(2) Complement of negative numbers: the sign bit is 1, and the remaining bits are the inverse of the original code of the absolute value of the number; then add 1 to the entire number .
      For example, the complement of -7: because it is a negative number, the sign bit is "1", and the whole is 10000111; the remaining 7 bits are the absolute value of -7 + the original code
     0000111 of 7, which is bitwise reversed to 1111000; plus 1, So -7's complement is 11111001.
Knowing the complement of a number, there are two operations to find the original code:
(1) If the sign bit of the complement is "0", it means it is a positive number, so the complement is the original code of the number.
(2) If the sign bit of the complement code is "1", it means that it is a negative number. The operation to find the original code can be: the sign bit is 1, the rest of the bits are inverted, and then the whole number is added by 1.
     For example, if one's complement is 11111001, the original code is 10000111 (-7): because the sign bit is "1", which means it is a negative number, this bit remains unchanged and remains "1"; the remaining 7 bits 1111001 are taken The reverse is 0000110; add 1, so it is 10000111.

　　90H is represented as 10010000 in binary, only the first digit of the complement of a negative number is 1, so X must be a negative number, and then change it into the original code of the absolute value, the method is: the sign bit is 1, and the rest of the bits are inverted, Then add 1 to the whole number

Then, it becomes 0111 0000, which is 112, so the absolute value of x is 56, and x is -56.