A few weeks ago I bought a Citizen 120D 9 pin printer off eBay. I used to own one of these printers, back in the good'ol days (early 90s). I bought one for the slightly insane reason of wanting to attach one to my little micro via a parallel port implemented with a 6522. I haven't actually done this yet. It seems slightly nutty to want to hook and print with such an old printer, when I have a perfectly good laser printer. But.... It's a hobby.

Anyway, the printer I bought is in near immaculate condition. The manual looks nearly new. It came with both a C64 interface module and the standard Centronics parallel port module. Because I'm so inclined, I opened up the parallel module. Noticed some big DIP parts but no numbers I was familar with, so I took a picture with my phone, put it all back together and decided I'd look up the parts some other time.

Here's the picture:



The 64pin shrink DIP took my interest. It is a M50734SP. Did some searching on the part and came up with this wikipedia article:

https://en.wikipedia.org/wiki/Mitsubishi_740

I'm aware that controllers are/were made around the 6502 instruction set, but this one is just gorgeous. It's got a UART, 24 IO pins, ADCs, multiple timers. And it's in CMOS (I think). And on top of that, it has the full CPU bus with control signals etc. The number of pins mean there's multiplexing involved, unfortunately.

The instruction set even has (I think) multiply and divide. I'm not a huge fan of the 6502 instruction set (please do not throw things at me...) but I can't help but be impressed.

So, questions:

Are these things or anything like them still made?
Am I missing some massive drawback here?
Why don't people use them in their projects?

It's a real shame the parts aren't socketed on that printer controller board, or I'd be inclined to try bread boarding one up since I have a Shrink DIP64 adapter made up, which I used with my V9558 work.

Anyway, I just wanted to share my little find.

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8 bit fun and games: https://www.aslak.net/

Howard Speegle, owner of Diva Automation, used the Mitsubishi 6502-based microcontrollers for many years in his products, but he said they got harder and harder to deal with, requiring larger and larger minimum order sizes, and he was forced to quit using them.

Dot-matrix impact printers do have a few advantages over modern laser printers. One is that you can print a line at a time and see it, without spitting out the rest of the page blank, and then you can print another line right below it several minutes later and see it, etc. (and of course keep the record, unlike the situation of it running off the display). Another advantage is that when I do program listings, I don't want page breaks interrupting structures and so on, so I like the fanfold paper. When proofreading, I like to do a continuous piece of paper that may be six feet long. I've kept a lot of old 9-pin printers, both the regular width and the double width, and also have a couple of really small ones for roll paper, one using 4.5"-wide paper and one using receipt strip. I've never had any trouble with these printers other than needing to replace the ribbons when they get light (which comes with plenty of warning, no catastrophic failures). The ink jet and laster printers we've had here have been temperamental, unpredictable, and rather expensive to use.

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

I have two of them attached to my Linux box, one being an Oki ML395 (wide) and the other an Oki ML520 (standard). Both are driven through the multiport serial interface.

Many businesses continue to use impact printers because they can generate multipart forms. Also, the cost per printed page is substantially less than it would be with a laser or ink jet unit. I have one client who has a Printronix line impact printer that prints faster than many lasers. They run all their forms through it, including disbursement and payroll checks.

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

I'd heard of that chip before, so I looked it up. There is a similar microcontroller in the Apple IIgs, it's used as the ADB controller. It's either a M50740 or M50741 depending on the IIgs. This is also a 64 pin SDIP, which is a lot of pins for an ADB controller. I guess the IIgs designers liked the idea of sticking with the 6502 instruction set.

The Macintosh SE and Mac II were the first Mac's to use ADB, but they used an 18 pin PIC for the controller, so no 6502 in a Mac.

(Welcome to the forum jds! It'd be great if you could post to the Introduce Yourself thread)