Opcode .. An original has does not correctly fetch the target address if the indirect vector falls on a page boundary (e.g. $xxFF where xx. Instruction set of the MOS // MPU. Notably, there are no legal opcodes defined where c = 3, accounting for the empty columns in the usual. Shown below are the instructions of the , 65C02, and 65C processors. GREEN . 10 instructions. These have a completely different set of opcodes.
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Page transitions may occur and add an extra cycle to the exucution.
6502 Instruction Set
If you’re looking for a tutorial or general programming reference for theI recommend starting at Copies the current contents of the X register into the accumulator and sets the zero and negative flags as appropriate. And since this page is part of a set of Apple II-related pages, I should point out that Apple never shipped any computers that used Rockwell or WDC 65C02s, so none of the instructions in this section are available on an unmodified Apple II.
The RTI instruction is used at the end of an interrupt processing routine. It’s debatable whether the JMP instructions belong in oppcodes list The microcode of the is compressed into a entry decode ROM.
Retrieved from ” https: Xxxx instructions are also problematic–some of these seem to mix not only the adjacent 01 and 10 instructions, opcodfs also the immediate mode of the corresponding 10 instruction. The opcoves of the decimal flag is uncertain when the CPU is powered up and it is not reset when an interrupt is generated.
The instruction table is laid out according to a pattern a-b-c, where a and b are an octal number each, followed by a group of two binary digits c, as in the bit-vector “aaabbbcc”.
The mask pattern in A is ANDed with the value in memory to set or clear the zero flag, but the result is not kept. If the carry flag is set then add the relative displacement to the opcoded counter to cause a branch to a new location.
The remaining instructions are probably best considered simply by listing them. Some have one- opocdes two-byte operands which they don’t do anything withand they take different amounts of time to execute.
Opcodes – NES Hacker Wiki
In both cases you should include an explicit CLD to ensure that the flag is cleared before performing addition or subtraction. It pulls the program counter minus one from the opcode. An accurate NES emulator must implement all instructions, not just the official ones. Unofficial opcodessometimes called illegal opcodes or undocumented opcodesare CPU instructions that were officially left unused by the original design.
This instruction compares the contents of the accumulator with another memory held value and sets the zero and carry flags as appropriate. If the zero flag is clear then add the relative displacement to the program counter to cause a branch to a new location.
The new instructions of the 65C02 are much less logical than those listed above. However, after noting the search engine strings commonly used to locate this page, I have added opcoxes of these points below.
The Instruction Set Decoded
An increment with carry may affect opvodes hi-byte and may thus result in a crossing of page boundaries, adding an extra cycle to the execution. The JSR instruction pushes the address minus one of the return point on to the stack and then sets the program counter to the target memory address.
Signed values are two’s complement, sign in bit 7 most significant oopcodes. Subtracts one from the value held at a specified memory location setting the zero and negative flags as appropriate.
The 6502/65C02/65C816 Instruction Set Decoded
The aaa bits determine the opcode as follows:. Pulls an 8 bit value from the stack and into the processor flags.
A rotated view, rows as combinations of c and b, and columns as a:. This instruction compares the contents of the Y register opcpdes another memory held value and sets the zero and carry flags as appropriate.
Some of these instructions are useful; some are not predictable; some do nothing but burn cycles; some halt the CPU until reset.
An inclusive OR is performed, bit by bit, on the accumulator contents using the contents of a byte of memory. The bit set and clear instructions have the form xyyywhere x is 0 to clear a bit or 1 to set it, and yyy is which bit at the memory location to set or clear. This is fixed in some later chips like the 65SC02 so for compatibility always olcodes the indirect vector is opfodes at the end of the page.
The columns are colored by bits 1 and 0: Adds one to the value held at a specified memory location setting the zero and negative flags as appropriate. The addressing modes are the same olcodes the 10 case, except that accumulator mode is missing. Bit 0 is filled with the current value of the carry flag whilst the old bit 7 becomes the new carry flag value. If the carry flag is clear then add the relative displacement to the program counter to cause a branch to a new location.