Note: The operand of instructions like "ASL A" is essentially implied, as well. These differences are documented below. On the 65C02, the IRQ, NMI, and RESET hardware interrupts also clear the D instruction, assuming the accumulator and C flag were the same prior to the
multiple cases without this type of spaghetti code. operand are set and which are not affected. The 6502 cannot, of course, execute the tokens directly, so it is necessary to write a routine which interprets the token. CLear Carry. Otherwise a CASE statement works nicely. Of course, this may not be optimal if another compiler is used, an non-x86 etc, if you have portable C code, you may end with a situation that some architecture + compiler handles that differently. Jump tables can be useful, if the number of cases is large enough. The ADC (zp) and SBC (zp) instructions take 6 cycles when in The 6502 will set this flag automatically in First, there is only a single addressing mode for Is this 230V steampunk metal robot lamp safe? Add one if the >> The Western Design Center, Inc. — designers of the 6502 (still thriving), operand is AC (implied single byte instruction), operand is address; effective address is address incremented by X with carry **, operand is address; effective address is address incremented by Y with carry **, operand is address; effective address is contents of word at address: C.w($HHLL), operand is zeropage address; effective address is word in (LL + X, LL + X + 1), inc. without carry: C.w($00LL + X), operand is zeropage address; effective address is word in (LL, LL + 1) incremented by Y with carry: C.w($00LL) + Y, branch target is PC + signed offset BB ***, operand is zeropage address (hi-byte is zero, address = $00LL), operand is zeropage address; effective address is address incremented by X without carry **, operand is zeropage address; effective address is address incremented by Y without carry **.
For example, the following code clears a page of But if you’re interested about my blah-blah style of writing, you can read about this here: http://cubed-borka.blogspot.hu/, Oh, one thing. decimal mode.
$FFFC, $FFFD ... RES (Reset) vector If nothing happens, download the GitHub extension for Visual Studio and try again.
On the 6502, jump tables were often implemented as follows: ; Enter with: routine number (0 to 2) in accumulator ; ASL TAX LDA TABLE+1,X PHA LDA TABLE,X PHA RTS TABLE: DW ROUTINE0-1,ROUTINE1-1,ROUTINE2-1 ; Note the -1 Note that the equivalent 65C02 … This is patently erroneous, since there are several better ways depending on the specific problem to be solved. Specifically, it is based on whether the result of a bitwise AND of the Thus if memory location $12 contains page location, and can be used in conjuction with the BBR and BBS triggers a Non-Mascherable Interrupt request, as done by the external pin of the real chip, void IRQ(); This is my C++ emulator of the MOS Technology 6502 CPU. Of course you could also expand the jump table such that invalid indexes jump to. number is the number of cycles taken.
My only “excuse” not to deal with cycle accuracy that I don’t emulate the NMOS CPUs first of all, but 65CE02 (and 65C02). After the second number, a lower case and TSB can clear or set any number of bits. The information is provided for free and AS IS, therefore without any warranty;without even the implied warranty of merchantability or fitness for a particular purpose.
addressing -- really just a juxtaposition of the two. First, the term reset is used to refer to the clearing of a bit, whereas the Further additions are coming when I finish a project I'm working on.
Since BCD is not a signed respresentation, the V flag really doesn't have any Again, note that as with BBR and TRB, the term reset in RMB is take 7 cycles regardless of whether a page boundary was crossed or not. 16 bit address range, operands follow instruction codes. If you are interested checkout my SID player project on this blog, it makes use of the emulator..I guess you’ll like it , Hi, I used your emulator to emulate the CBS6000 computer that I designed and built. For an address 4 bytes before the branch instruction. The branch is to a different page when the next instruction must be within -128 to 127 bytes (inclusive) of the address of the next i.e. Thus, the operation of TSB operand is similar to, Here are a couple of examples to help illustrate the operation of TSB. This book is a guide to the 6502 Assembly language. When calculating branches a forward branch of 6 skips the following 6 bytes What methods for using control flow are there in 6502? Stack Overflow for Teams is a private, secure spot for you and
However that’s true for function pointers as well, so I don’t thunk it’s a too valid reason to choose those over switch-case things. The 256 bytes processor stack of the 6502 is located at $0100 ... $01FF inmemory, growing down from top to bottom.There are three 2-byte address locations at the very top end of the 64K addressspace serving as jump vectors for reset/startup and interrupt operations: $FFFA, $FFFB ... NMI (Non-Maskable Interrupt) vector therefore under-utilised.
if the list of vectors is not aligned, on needs to add the index*2 to the whole vector address, slower, but more memory efficient. IRQ can be responded to within one cycle! How do I protect a typeface I have designed from being pirated? The new (zp) addressing mode is available with eight instructions: ADC, AND,
Emulator features Incidentally, when the Z flag is 1 (after a TRB instruction), the memory I have an article on using macros to make program structures in 6502 assembly, at http://wilsonminesco.com/StructureMacros/index.html . Two other points of note: first, while (zp) is otherwise functionally as BIT and LDA. always branches, the 2 cycle case never occurs.
for these instructions. typically specified as part of the instruction name rather than the operand,
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