@Arlet Thanks for the explanation. Everything make sense now

Here are the simulation waveforms.

As can be seen when RDY becomes zero, it is as if the a9 (which is an LDA) is discarded. When RDY becomes one again in the other waveform, the system assumes 20 is the opcode (which is an actual fact the operand of the LDA), being a JSR. One can also see ...

I used the original 6502 core from Arlet Ottens in a number of projects and had great fun with this core.

Recently I was working on a project where I was implementing some DMA where I needed to pause the 6502 CPU core (via the RDY signal) while transfer took place from DMA to memory, in which I ...

Very interesting thread.

Regarding which 6502 software I use often. I was actually a bit shocked since the last two years I haven't actually used any 6502 software. Towards the end of lockdown my day job became more busy and I couldn't get around playing with 6502 stuff.

Earlier on in the lockdown ...

Thanks everyone. It makes sense that they probably used a tool like patch/diff.

These kind of history always interest me.

Greetings

I recently stumbled across this video: https://youtu.be/roBkg-iPrbw

This video is about how Soundtracker evolved on the Amiga.

Although the cracking and reverse engineering of the original commercial software was probably not so legal :), it is still amazing to see, with the combined ...

Thanks for the info @ttlworks. This was exactly what I was looking for!

There is pretty ample information available for most custom Commodore chips. For some chips, like the PLA on the C64, there is no datasheet available, but for these there was some reverse engineering efforts.

One custom CSG chip I cannot find any information about is the Disk Controller Chip for ...

Hi All

It has been quite while since I posted an update in this thread on my progress with this project.

I have actually been making some good progress and this module can currently boot the C64 and display on the VGA screen. You can also play a game and use an USB keyboard to interact with the ...

Around 1984, an Assembler named CHAMP was published with versions that could run on the C64, ZX Spectrum, and BBC Micro.

Here is a copy of the original documentation:
http://www.worldofspectrum.org/pub/sinclair/games-info/c/Champ.pdf

On the Internet I can only get hold of a ZX spectrum tape ...

Vice is also a nice alternative. When you compile from source with the debug option, you get an extra menu option "debug" which allows you to enable tracing of the main cpu. The trace include a dissasembled trace of the instructions executed, together with the state of all the registers and cycle ...

Hi Arne

Thanks for the explanation, but I see you are actually referring to the playback scenario.

The scenario I am actually after is the recording scenario, that is when the switch next to R/W Head is in the REC position and Write data enters from the right, and also via the REC switch position ...

Hi All

The following article on Wikipedia gives some information on how the 1530 Datasette worked:

https://en.wikipedia.org/wiki/Commodore_Datasette

Some detail is given on how the analog data on cassette was converted to digital data with which the Commodore 64 could work with.

However some ...

I can actually assosiate with the kind of pain you went through with the use of two clock frequencies in your system.

Recently I wanted to make a VGA implementation that displays a frame stored in SDRAM.

The catch here was that the pixel clock was running at 85.4MHz and the memory subsystem ...

I have just released the next post in my series on creating a C64 on an FPGA with the Zybo Board. In this post we attempt to display a frame from SDRAM to the VGA.

Here is the link:

http://c64onfpga.blogspot.com/2018/06/dddd.html