Contents
Which flag is set when ALU generates complete zero result?
Along with a carry flag, a sign flag and an overflow flag, the zero flag is used to check the result of an arithmetic operation, including bitwise logical instructions. It is set to 1, or true, if an arithmetic result is zero, and reset otherwise.
How do you find a zero flag?
The 5 flags are:
- Sign Flag (S) – After any operation if the MSB (B(7)) of the result is 1, it indicates the number is negative and the sign flag becomes set, i.e. 1.
- Zero Flag (Z) – After any arithmetical or logical operation if the result is 0 (00)H, the zero flag becomes set i.e. 1, otherwise it becomes reset i.e. 0.
How4 bit ALU works?
Each operand has 4 bits of low latch and 4 bits of high latch, to store 8 bits. The two operands go to the “alu core”, which performs the desired operation: addition, logical AND, logical OR, or logical XOR. The ALU first performs one computation on the low bits, storing the 4-bit result into the result low latch.
What is the status of zero flag when the result of an arithmetic operation is zero?
For example, if the result of an arithmetic operation is zero, the zero flag is set (i.e., ZF = 1). Once a flag is set or cleared, it remains in that state until another instruction changes its value. Note that not all assembly language instructions affect all the flags.
What does a 0 in the zero flag after an arithmetic operation mean?
Zero flag (ZF) – the zero flag is set(1) when the result of an arithmetic operation is zero. Unsigned overflow means there has been a carry out of, or a borrow into, the most significant bit (msb) of the destination operand in an arithmetic operation using unsigned numbers.
Which flag get set when the result is zero?
Zero flag (ZF) – the zero flag is set(1) when the result of an arithmetic operation is zero. Sign flag (SF) – the sign flag is set(1) when the result of an arithmetic operation has a 1 in the most significant bit (msb)….
| Status Flags | Flag Set (1) | Flag Clear (0) |
|---|---|---|
| OF | OV | NV |
Which instruction type affects the flag?
As there is no arithmetic or logical operation being performed, no flags are affected by data transfer instructions. Arithmetic instruction: Arithmetic Instructions are the instructions that perform basic arithmetic operations such as addition, subtraction, and a few more.
What is the function of auxiliary carry flag?
The Auxiliary flag is set (to 1) if during an “add” operation there is a carry from the low nibble (lowest four bits) to the high nibble (upper four bits), or a borrow from the high nibble to the low nibble, in the low-order 8-bit portion, during a subtraction.
How is the zero flag generated in the ALU?
The zero flag is generated in the ALU by NOR of all 8 bits: the 4 bits that were just generated by the ALU, and the 4 bits that are latched in the ALU from the previous half-operation. Carry on the other hand is much more complicated. The 4-bit operation generates the half carry, which is latched.
How does the ALU work on the Z-80?
The Z-80 provides extensive bit-addressed operations, allowing a single bit in a byte to be set, reset, or tested. In a bit-addressed operation, bits 5, 4, and 3 of the instruction select which of the 8 bits to use. On the far right of the ALU block diagram is the bit select circuit that support these operations.
How does the carry work in the Z-80?
The carry from the first computation is used in the second computation if needed. The Z-80 provides extensive bit-addressed operations, allowing a single bit in a byte to be set, reset, or tested. In a bit-addressed operation, bits 5, 4, and 3 of the instruction select which of the 8 bits to use.
How does the shift circuit on a Z-80 work?
The Z-80 in comparison performs a shift while loading a value into the ALU. While the Z-80 reads a value from the register bus, the shift circuit selects which lines from the register bus to use. The circuit loads the value unchanged, shifted left one bit, or shifted right one bit.