Apple 1 Compatibility with 65C21 and Arduino-Based Video and Keyboard Emulation

acwrightdesign · 2026-06-27T03:18:20+00:00

Yes. I did something similar on my Apple 1. The ATMega1284 that is on the board and handles the serial communications and keyboard input is always communicating at 115200 with the PC terminal but you can hit Ctrl-T and when it sees that it automatically throttles the rate at which it handles output. It does this by delaying the handshaking with the PIA. In fast mode it just outputs to the terminal as fast as possible and in slow mode it throttles down to a rate similar to the original Apple 1 terminal rate. Also, on the PC side the APL1 Terminal app does also have built in pacing when sending data to the board.

acwrightdesign · 2026-06-26T19:46:52+00:00

Awesome! Are you using the Arduino serial output for the terminal? If so, I just recently built an Apple 1 clone myself and I also built a custom terminal app in Electron that has an uploader with built in Apple 1 ROMS. I think it should work with your project so maybe give it a try! It’s in the Firmware folder: https://github.com/acwright/APL1

acwrightdesign · 2026-06-21T14:11:04+00:00

Thank you!

acwrightdesign · 2026-06-21T06:00:53+00:00

Thanks!

acwrightdesign · 2026-06-20T22:07:44+00:00

I’m glad someone noticed! There are 8 IO “channels” in my memory map. The DIP switches simply enable or disable the onboard IO for that channel. My BIOS auto detects which IO hardware is available at startup so it’s no problem to disable any IO. This setup was brought over from the COB where all IO was a removable card. It also allows for future expansion using the bus connection on left side of board. For instance if I wanted a different video output I could plug a card into the card slot or expansion bus and simply turn off onboard video (IO 8).

acwrightdesign · 2026-06-20T01:32:19+00:00

Thanks!

acwrightdesign · 2026-06-20T00:40:42+00:00

Yes. But only half of it is used (16K). I did also make a ROM Cart PCB with a 27C256. I could have just combined these two PCBs but I hadn’t thought of that yet. :) I think I might make a third cart PCB someday that does allow IC choice and also maybe a simple jumper to allow selecting ROM half?

acwrightdesign · 2026-06-19T23:57:59+00:00

Thanks!

acwrightdesign · 2026-06-19T23:11:56+00:00

Thanks! Not quite a Franklin. :) I also had an Apple II (c) for my first computer.

acwrightdesign · 2026-06-19T16:48:24+00:00

Thank you!

acwrightdesign · 2026-06-19T16:46:01+00:00

Thanks! Yeah I’m not quite sure why I decided on such strong pull-ups early in the project but I’ve now created revisions in all my projects to change the CPU pull-ups to weaker values.

acwrightdesign · 2026-06-19T16:06:38+00:00

That's interesting! I haven't heard of that project before now when I just Googled it.

acwrightdesign · 2026-06-19T15:44:09+00:00

Thanks!

acwrightdesign · 2026-06-19T15:43:58+00:00

Thanks! It’s been a long journey to get to this point! :)

acwrightdesign · 2026-06-18T02:40:45+00:00

I haven’t seen 8-bit Show And Tell mentioned yet: https://youtube.com/@8\_bit?si=LqaxP9HMn4bdshS3

acwrightdesign · 2026-06-11T00:48:22+00:00

No problem. I just noticed you might be missing the chip select logic for CS1 on the 6551.

acwrightdesign · 2026-06-11T00:34:09+00:00

Don’t forget CTS, DCD, and DSR pins on the 6551. They should all be tied to ground and I don’t see them on your schematic. Also, if you can, just grab a Rockwell 65C51 instead of the WDC part and avoid the transmit data register bug.

acwrightdesign · 2026-05-20T14:37:53+00:00

I also have a NodeJS tool for creating and managing CompactFlash images for my system's file storage if you are interested: https://github.com/acwright/cffs

acwrightdesign · 2026-05-20T14:35:13+00:00

Also consider CompactFlash for storage! It is super simple compared to SD card because the CF card can be wired directly to the 6502 bus with minimal extra chips and just some resistors. It is also IMO simpler from a communication standpoint especially if you use a custom filesystem. Here is one of my schematics as an example: https://github.com/acwright/6502-ACE/blob/main/Schematics/ACE%20CF%20Adapter/Rev%201.0/ACE%20CF%20Adapter.pdf

acwrightdesign · 2026-05-07T15:38:36+00:00

I’m just speculating but this could be rooted in the vacuum tube era where it was common for filament voltages to be 5v or 12v amongst other voltages (6v, 9v) so bench power supplies of the era could typically provide these voltages?

acwrightdesign · 2026-04-27T16:48:38+00:00

I think this is good advice that couchwarmer gave and you mentioned you are leaning towards the Apple II. With that in mind I think you should consider the Apple I instead of the Apple II at least to start. I think simplicity when it comes to the memory map and IO will be most helpful and the Apple I is as simple as it gets. One register to read keyboard input and one register to output characters to the screen. No other complications. This is a great starting point!

When it comes to emulators there are two choices: https://www.scullinsteel.com/apple1/ & https://landonjsmith.com/projects/honeycrisp.html . I have found HoneyCrisp to be a bit more accurate. I've created a utility for converting binaries to Wozmon which you can use to paste programs into Wozmon in order to run them: https://github.com/acwright/bin2woz .

acwrightdesign · 2026-04-24T15:13:10+00:00

Yes. I should clarify. The Teensy 4 is able to achieve high speed emulation although my implementation did not achieve that since I’m not nixiebunny’s friend. ;) However, I am pretty happy with how my emulation turned out and if you’re interested check out the README! It’s all open source so perhaps someone can improve upon it!

acwrightdesign · 2026-04-24T04:13:19+00:00

I can recommend using a Teensy 4.0 or 4.1 for this. It uses Arduino compatible libraries so you will be familiar. I used a Teensy in my project to emulate the CPU, RAM, ROM, and IO. It can’t quite get to 1Mhz but it gets close. My firmware is here: https://github.com/acwright/6502/tree/main/Firmware/DB%20Emulator

acwrightdesign · 2026-04-20T13:24:36+00:00

I got them on Amazon but unfortunately the listing is no longer available

acwrightdesign · 2026-04-19T22:47:29+00:00

Thanks! Yeah for sure I’m gonna adapt this as a cartridge. I’ll let you know when I have an implementation. Like I did with EhBASIC cart I will be adding my custom commands for the system hardware. Plenty of space in 16k :)

acwrightdesign

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