How many instructions does 6502 have?
How many instructions does 6502 have?
Of the 256 possible opcodes available using an 8-bit pattern, the original 6502 uses 151 of them, organized into 56 instructions with (possibly) multiple addressing modes. Depending on the instruction and addressing mode, the opcode may require zero, one or two additional bytes for operands.
What is the stack 6502?
Stack pointer is a variable that holds the current index of stack. In 6502 assembly, it’s an number which sets the boundary between used and unsued stack elements. In a 6502 microprocessor, stack is hardcoded between the memory addresses $0100 and $01FF. And it’s in the zeroeth page of the memory.
Are 6502 processors still used?
It’s Still in Production These are being used in all sorts of commercial devices, including external sound interfaces from companies like MOTU, medical devices and scanners, hand-held games and more. Bill Mensch is one of the holders of the 6502 patent, so who better to work on it today than him.
What do opcodes do?
An opcode identifies which basic computer operation in the instruction set is to be performed. It is used when writing machine code. It tells the computer to do something. Each machine language instruction typically has both an opcode and operands.
How do you use opcodes?
The opcode is the instruction that is executed by the CPU and the operand is the data or memory location used to execute that instruction….Opcodes and operands.
| Assembly language opcode mnemonics and instructions | Meaning/use |
|---|---|
| ADD (Add) | Adds accumulator contents to the contents at a RAM address |
How does a CPU stack work?
A stack (also called a pushdown stack) operates in a last-in/first-out sense. When a new data item is entered or “pushed” onto the top of a stack, the stack pointer increments to the next physical memory address, and the new item is copied to that address.
How does the 6502 program counter work?
When the 6502 is ready for the next instruction it increments the program counter before fetching the instruction. Once it has the op code, it increments the program counter by the length of the operand, if any.
Is the 6502 instruction set broken into regular patterns?
Though the 6502 instruction set has a number of quirks and irregularities, large portions of it can be broken up into regular patterns.
What is the difference between the 65C02 and the NMOS 6502?
The 65C02 has many similarities to the NMOS 6502, but the 65C02 has additional instructions and addressing modes available. In addition, there are instructions with functional differences and different cycle counts.
What do the flags mean on the 6502 microcontroller?
The Decimal flag controls how the 6502 adds and subtracts. If set, arithmetic is carried out in packed binary coded decimal. This flag is unchanged by interrupts and is unknown on power-up. The implication is that a CLD should be included in boot or interrupt coding. The Overflow flag is generally misunderstood and therefore under-utilised.
