I am having difficulties with understanding what's going on in this code:
LD A, -1;
LD B, 130;
ADD A, B;
And what flags are set to 1 after the ADD instruction.
Basically, I don't know, what value is stored inside the register B.
I cannot find any information whether 130 in LD B, 130 means "1000 0010" or "0 1000 0010" (so subsequently we've got to get rid of the MSB/LSB - I don't know which one).
As a result, I am not sure what is the final value stored in A.
The Z80 is an 8-bit processor, therefore your 9-bit number 0 1000 0010 has no relevance. The code you posted
LD A, -1;
LD B, 130;
ADD A, B;
is equivalent to
LD A, 0hFF
LD B, 0h82
ADD A, B
and after the addition register A will contain 0h81
The addition will cause the Carry flag to be set, since it generates a "borrow". The Carry is a result of unsigned addition.
It will cause the Overflow flag to be clear, since there is no "internal carry" from bit 6 to bit 7. Both values were negative to start, and A remains negative. The Overflow Flag is set when the signed sum cannot be represented in the register correctly.
The Zero Flag will be clear, since A is non zero.
The Sign Flag will be set, since A is negative according to bit 7.