Hi to all,
I haven't written here for a long time. Since I built my Apple 1 Replica. A few years later, here I am again with a new project. A Macintosh 128k Replica, but this time my aim is to tackle this project to keep myself busy, due to health issues.
This is an ambitious project, full of topics to discuss and discover that I have decided to share. With me a special collaborator, ChatGPT who will help me speed up the search for information.
Obviously, I would be very happy if you participate with comments and ideas. I hope you will find this blog motivating, useful and fun.
https://macintosh-replica-story.blogspot.com/?m=1
Ambitious project. Although outside links are welcome, we don't allow post that are just ads/announcements (AUP: 3.d). This forum is intended to become a perpetual resource, so whenever possible, please provide as much context in each post as possible. Extensive attachments are welcome.
I am sorry, But if I am allowed, It's my intention to share here periodic summaries of the posts in the blog.
The post should be able to stand on its own, once the off-site material is no longer available. So many of our early forum posts have become useless, because we didn't do it this way in the past.
Sure, it makes sense. I understand. I will summarize milestones of the project here with images and docs hosted here.
Hi to all,
after a couple of weeks of "work" on my Macintosh replica project, I felt like I entered the hole of the white rabbit. I am finding new and interesting things day by day, and this adventure is going to be a big challenge, a personal challenge. That said, I have found several docs about the hardware of the early family of Macs, but it's not that easy to figure out if those docs belong to prototypes or commercial models. I want to focus on the first Mac in the market. Now, I want to be sure that the first model is the Macintosh 128k.
Regarding this, I wanted to understand if the "128k" refers to the maximum amount of bytes of DRAM (64K High bytes + 64K Low bytes). The Doubt is Because I have read about a 64K Model of Macintosh, and I don't know if the authors of the articles know what they are talking about or not... I mean, did they say "64K" because they read this value on a schematic (but they didn't understand that there are 2 banks) ?
What is killing me are the PALs: BMUs, VIA, SCC, etc, It's not clear if they are different from model to model. I would like to find the truth tables of them or reverse-engineering them. That's why I started to search a logic board of a Macintosh 128k, even defective, I want to desolder Pals and test them separately.
Is there anybody who has one to donate to the science?
Thank you.
I will share the results of my research here: code, truth tables, etc. So I hope somebody can help me.
The first Macintosh models—the Macintosh, which had 128KB RAM and the Macintosh 512K (or "Fat Mac") both had the original 64KB ROMs. The next model was the Macintosh Plus which used 128KB ROMs. Among the additions to the larger ROM was support for the HFS file system and SCSI disks, which had limited support on the earlier computers: the former required booting from a 400KB disk with the so-called "HD20 INIT", and the latter was not supported at all outside of a few uncommon third-party expansions that piggy-backed on the MC68000 chip.
So both the Macintosh and the Macintosh 512K could be referred to as having the 64KB firmware, which was a very specific limitation with deeper implications than merely the amount of RAM available.
After the Macintosh Plus was introduced, there was an upgrade available for the 512K to what was called the "Macintosh 512K Enhanced" (or "512KE") that provided the Plus's 128KB ROM. So a Macintosh 512K found today could have either the 64KB or the 128KB ROM in it. That upgrade was not officially available for the original Macintosh, but it could have been bodged in by third-party technicians I suppose.
The VIA and SCC are not PALs: they are off-the-shelf integrated circuits, from Rockwell and Zilog, respectively, and are fully documented (as far as that goes) in their datasheets. The IWM, BBU and GLU chips in early Macintosh models are the only ones that were custom. Later, with the Macintosh SE, a custom microcontroller for the ADB bus was also used.
Thanks for the explanation.
I've been researching technical details about the Apple Macintosh 128k hardware, particularly the custom PAL chips (BMU1, LAG, BMU0, TSM, ASG). The 'Inside Macintosh' document provides some information, but additional research revealed specifics:
These chips play crucial roles in the Macintosh 128k's operation, contributing to its efficiency. Emulating their precise functionality requires studying the original truth tables, which is challenging. Currently, I'm focusing on exploring the memory map for further understanding.
mac-logic-schematic.jpg
Great information, I can't add anything to that.
Note, though, that the floppy speed /PWM signal was only used for the original Sony OA-D34V drive. Later drives made the speed control internal, and the /PWM pin on the cable was not connected anymore.
That's interesting!
Hi to all. My Apple #macintosh replica project is moving forward. It is keeping me busy and #alive as I wished, and it is becoming an exciting journey. The Mac 128k was an incredible machine for the early #80s, and I am enjoying this self-learning long session.
I am now working on the custom chips present in the Mac. Six #PALs "Programmable Logic Array" that manage all base functions. I have found a tool that I want to bring your #attention to. It is a digital circuit simulator, in my opinion, one of the best I have ever seen.
I warmly suggest you check it out!
This tool will help me understand all the dynamics needed to develop the emulator for the STMicroelectronics #stm32h7 #microcontroller.
I will publish some progress with Mac reverse engineering in my blog very soon!
FB_IMG_1700213195681.jpg
Hi to all,another post on my Apple #macintosh 128k replica project. I am really enjoying the time spent on reverse engineering this incredible computer. As I mentioned in some previous posts, I am using the #Digital #circuit #simulator to build areas of the #logic #mainboard and check how the #Mac works.The video below shows the virtual circuit that I built to test the "pixels streamer" of the #video #circuitry. It is made by a chain of two shift registers, where two bytes read from #RAM (in my simulation I used #EEPROMs) are latched and shifted out every pixel clock pulse.As a virtual #display, I've used the graphic RAM component, very easy to handle.I am very excited about this tool and what I understand so far about the Macintosh. I am going to prepare some technical posts for my #blog.
Macintosh-video-circuitry.mp4