How many opcodes does the 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 are illegal instructions?
Illegal Instruction errors occur when you try to run a program that was compiled with some processor-specific optimizations, and is then running on a processor that fails to meet those requirements.
How many opcodes does the NES have?
The opcode is a byte value in the range 0 to 255 inclusive. The 6502 supports 151 opcodes and they are grouped into 56 operations. Each opcode in a group performs the same basic operation, such as adding two numbers together.
Which of the following instruction is not valid Mcq?
4. Which of the following instruction is not valid? Explanation: Both the source and destination operands cannot be memory locations except for string instructions. Explanation: The actual current stack-top is always occupied by the previously pushed data.
What refers to an illegal instruction into a computer system or network?
Answer: Hacking means an illegal intrusion into a computer system or network.
What is meant by opcodes?
In computing, an opcode (abbreviated from operation code, also known as instruction machine code, instruction code, instruction syllable, instruction parcel or opstring) is the portion of a machine language instruction that specifies the operation to be performed.
Why does the 6502 have zero page opcodes?
The use of zero or zero page values will result in assembled code with zero page opcodes when you wanted absolute codes. With $FFFF, the problem is in addresses+1 as you wrap around to page 0. When the 6502 is ready for the next instruction it increments the program counter before fetching the instruction.
What does the interrupt flag do on the 6502?
The Interrupt flag is used to prevent (SEI) or enable (CLI) maskable interrupts (aka IRQ’s). It does not signal the presence or absence of an interrupt condition. The 6502 will set this flag automatically in response to an interrupt and restore it to its prior status on completion of the interrupt service routine.
When does the 6502 increment the program counter?
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.
Which is part of the 6502 memory is called Zeropage?
65CE02: Extension of the 65C02, used in the C65. The first 256 bytes of adressable memory are called Zeropage. The 6502 processor family offers a wide selection of adressing modes to work with this part of the memory, which generally results in shorter and (even more important) faster code.