Breaking 6502 apart

[BigEd]

These are individual columns of the decoder PLA, each being a big NOR gate. The IR is the Instruction Register.

[org]

Yeap, and BRK2 / JSR3 are decoder line names. Number after opcode represent cycle, when this decoder line is trigger.

[org]

I almost completed top part on logic gates, and made some draft of it.

Don't look closely, it may contain typos and still not fully "de-morganized", just wanted to show you complexity and structural parts of it.

Bottom part will be done after top one.

[BigEd]

Bravo!

[org]

Todays speccy: ALU control

(I'm lazy to complete PLA lines, will be added later )

+fixed shortcut on ROR carry logic in transistor circuit.

[org]

Updated and cleaned up most of circuits on http://www.circuitlab.com

Need to add some missing parts of bus control and top part will be ready.

6502.org wrote:

Image no longer available: https://www.circuitlab.com/circuit/2b9sy6/screenshot/540x405/

[org]

Ok, I'm done with top part.

I isolated 6502 "core" and trying to understand how its executing, step by step.

Some slides below

[org]

Updated transistor circuits. Fixed some errors and split it on two parts : top and bottom.

[org]

In last minutes I found missing part of DL/DB, will be fixed soon )

[org]

Todays speccy: ALU logic circuit

Later I maybe optimize SUM calculation, by replacing couple of NAND/NORs by XORs.
Don't want to mess with inverted carry chain ATM

[whartung]

Hi org,

I just wanted to congratulate you on the 1 year anniversary of this project (I know, I missed it by a day). Hard to believe it's been a year, but here it is, and you're still going strong on it and making great progress from the looks of things (not that I have really any idea what I'm looking at).

But kudos to perseverance.

[BigEd]

Great progress indeed - happy yesterbirthday to the project

[org]

Thank you, I really appreciated for your support !

Within few days I'm going to complete whole 6502 logic circuit.

Today I experimented a bit with GIS applications, and adapted it for my task: http://breaknes.com/files/6502/tilemap/
This is tile map viewer of extra-large images, based on OpenLayers API.

[BigEd]

I like it! (Did you see the 65CE02 post? There's a slippy map there of the die shot.)

[org]

Todays speccy: Program Counter logic circuit