How is the offset of a relative branch calculated?

How is the offset of a relative branch calculated?

The branch offset is computed as the number of words between the branch instruction and the branch target. This byte offset will be added to the current contents of the PC to produce the branch target address.

What is 6502 assembly?

6502 assembly is a very low-level language that works specifically for the 6502 microprocessor — a very popular processor from the 1970s.

How is the branch address calculated?

A branch instruction computes the target address in one of four ways:

• Target address is the sum of a constant and the address of the branch instruction itself.
• Target address is the absolute address given as an operand to the instruction.
• Target address is the address found in the Link Register.

What is the target branch address?

The branch target address is the address of the next instruction if the branch evaluates as taken. Some branch instructions include the branch target address in the instruction op-code, or include an offset whereby the branch target address can be easily calculated.

What is a branch instruction in MIPS?

Branch instructions use a signed 16-bit offset field; hence they can jump instructions (not bytes) forward or. instructions backwards. The jump instruction contains a 26 bit address field.

How is offset address calculated?

2. offset = A mod page_size

1. this is the distance from the beginning of the page.
2. e.g. address in the process, A = 10,000.
3. page size = 4k.
4. page offset = 10000 mod 4k = 10,000 mod 4096 = 1908.
5. this calculation is done quickly on the computer since the page size is power of 2, e.g., 4k = 2^12.

How does the 2 cycle branch work in the 6502?

The 6502 has a two-stage “pipeline” for instruction decoding, so the opcode for the next is already fetched in the last cycle of the current instruction. This is how the 2 cycle variant of branch works: One cycle for opcode fetch, one cycle to fetch the offset, and if the branch is not taken, then the next opcode is just fetched normally.

How does the MOS 6502 implement its branch?

Enter a branch, and watch what the control lines do. You can even see where every signal is located on the chip. The 6502 has a two-stage “pipeline” for instruction decoding, so the opcode for the next is already fetched in the last cycle of the current instruction.

When to use relative relative addressing on 6502?

Relative Relative addressing on the 6502 is only used for branch operations. The byte after the opcode is the branch offset. If the branch is taken, the new address will the the current PC plus the offset. The offset is a signed byte, so it can jump a maximum of 127 bytes forward, or 128 bytes backward.

How to see what happens in the 6502?

You can see exactly what happens in the 6502 using the in-browser simulation provided by visual6502.org in advanced mode. Enter a branch, and watch what the control lines do. You can even see where every signal is located on the chip.