That's totally ok! I totally agree with you about ambiguity and technical language. I am still able to edit my post on medium, when I get a chance I will go over what I wrote and take into account what you said. Thanks!

Hey all,
After spending some time learning assembly I have tried to write some posts aimed at someone who has never seen any low-level programming language before. I posted it on r/learnprogramming last week and it got a good reaction from people, so I thought I'd try sharing it here too. I have a ...

It's an interesting question -although an odd one

I think maybe I've got myself confused over something that maybe doesn't matter to much then haha I have been thinking of the Overflow flag as a way to "fix" the error - is that maybe not the best way to think of it? Is it just rather a way to ...

Without specifically answering your question, allow me to direct you to the following excellent tutorials by 6502.org's own Bruce Clark. :)

The Overflow (V) Flag Explained

Beyond 8-bit Unsigned Comparisons


-- Jeff

Thanks for the response!
I've been reading through these just now and I ...

I am trying to really nail down how overflow works. If you add 2 signed numbers and the result should be >127 or <-128 this will cause an overflow (kinda like carry for an unsigned number more than 256).

I have been reading this: http://www.righto.com/2012/12/the-6502-overflow-flag-explained.html ...

Back in those early days, I generally bought many of the books published by OSBORNE/McGraw-Hill. Computing books in general, the CRT controller handbook and some of the books from Lance Leventhal (6502 and Z80). One of my favorites is the 6502 Assembly Language Subroutines co-authored by Winthrop ...

INC (POINTER) is not a valid 6502 instruction. Could that be a typo perchance?

Sorry, that was my fault. It is written as INC POINTER. I've double checked though, the rest is as it is in the book. I hadn't realised what you pointed out about the stack pointer wrapping, its something I'll keep in ...

In Programming the 6502 there is a chapter on IO techniques. Zak's shows a piece of code like this:


LDX COUNT
WATCH LDA STATUS
BPL WATCH
LDA INPUT
PHA
DEX
BNE WATCH


I feel I understand this, it "watches" STATUS, then when bit 7 is one, it transfers INPUT to the stack, decreases X, then ...

LDA #$05 ; these 4 lines put $0205 into p0
STA $01
LDA #$02
STA $02

LDY #05
lowList: ; deal with 5 to 1
TYA
STA ($01),Y
DEY
BNE lowList

LDX #15
LDY #05
highList: ; deal with 15 to 11
TXA
INY
STA ($01),Y
DEX
CPX #10
BCS highList ; if X > 10, loop

LDY #10 ; reload Y
LDA ($01),Y ...

So, I've made some changes. I'm a little busy at work at the moment, so I haven't been able to implement everything.


LDX #05
LDY #00
lowList: ; deal with 5 to 1
TXA
INY
STA $0205, Y
DEX
BNE lowList
LDX #15
highList: ; deal with 15 to 11
TXA
INY
STA $0205, Y
DEX
CPX #10
BCS highList ...

I notice you have one or two cases of branching over a jump: often you can swap those two instructions for a single branch, of the opposite sense.
That makes sense, I've changed the code to do that now.

So, if you have any register transfers like TYA or similar, there's a fair chance you can ...

Hey Everyone!
This is my first post here, hopefully this style of question is ok, if not I can post elsewhere or change it a bit.
I've been working through Rodney Zak's book Programming the 6502, and attempting the questions within in. One question asks the reader to write some code to find the ...