Electronics > Projects, Designs, and Technical Stuff

Cloning a Commodore PET-2001

<< < (15/33) > >>

GK:
Okay!!, attempt #2. I've modified the program to insert a short silence between played notes, so that the notes don't audibly run in to each other.  It sounds much more musical now. Note that in the original BBC Micro listing this was achieved with the additional empty SOUND statement on program line 190.

The short inter-note silence duration is determined by the new variable MUTE. I mute the audio by toggling the SR data byte between 15dec (ON) and zero (OFF).

Here is the tune mp3: https://www.eevblog.com/forum/projects/otp-eprom-programmer/?action=dlattach;attach=340954
   

MK14:
Here you go...

Bicurico:
Just to shout how fantastic this thread is.

What would be the cost involved in getting the required components and PCB to rebuild your design?

Regards,
Vitor

GK:
Oh, thanks for the interest. I missed this one - have been busy with other things the past few months. Dunno about total cost - parts alone for what follows were ~$80 AUD. Parts for the motherboard will probably be in the $100-$150 range. Then there is board fabrication, housing, etc.

Getting back to this project again; I've decided to modularise the design. The video graphics generator circuitry complete is now contained on a separate board. Communication to the mother (processor) board is via a 50-pin IDC header. I just finished the PCB layout this morning; will triple check everything over this evening and then send the design off the Elecrow.

The video graphics/character generator is a stand-alone project in its own right; could be used for any other project where you want to implement a retro 50 Hz video display. Except for the DIP EEPROM and (motherboard specific) DIP CPU/PIA/VIA all electronic components are SMD. I didn't endeavor to make the board ultra compact but rather basic to solder and compatible with even the cheapest PCB fab - 10 thou minimum track clearance (20-thou set for the GND polygon pour), all layed out on a 50-thou grid.  1206 passives, all logic ICs are SOIC and it's SOJ for the SRAM rather than TTSOP.

Now onto the motherboard.........



GK:
Hmm, this project got delayed a bit... I received my video generator board in the post yesterday, having only sent the Gerber files to Elecrow on the 16th. This evening I soldered it up and stitched it into my prototype computer, discarding the original through-hole video generation circuitry built up on prototype board.

Works like a charm. Up until now (due to the crappy construction) my prototype computer continued to suffer the occasional hangup due to signal integrity issues (mostly ground) associated with reading and writing the video RAM, which I never managed to fully resolve in the original build. These signal integrity issued also caused the computer to not boot reliably on each and every power-up in all available versions of BASIC.

Now that I've got the video generation circuitry all built up nice and proper on a properly layed out PCB, all of these issues are now finally resolved. I've been putting the computer through its paces and it refuses to miss a beat. The reason for the huge 50-way ribbon for communications to the motherboard is that every second wire is GND. This video board also serves as the master clock source for the CPU.

I hope to have the motherboard circuitry transferred to a (mostly SMD) PCB within a month or two. In the photo below the smaller proto board with the two DIP40s on it is the current PS-2 keyboard interface.





Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod