A 6502 Retrocomputer In A Very Tidy Package

One of the designers whose work we see constantly in the world of retrocomputing is [Grant Searle], whose work on minimal chip count microcomputers has spawned a host of implementations across several processor families.

Often a retrocomputer is by necessity quite large, as an inevitable consequence of having integrated circuits in the period-correct dual-in-line packages with 0.1″ spaced pins. Back in the day there were few micros whose PCBs were smaller than a Eurocard (100 mm x 160 mm, 4″ x 6.3″), and many boasted PCBs much larger.

[Mark Feldman] though has taken a [Grant Searle] 6502 design and fitted it into a much smaller footprint through ingenious use of two stacked Perf+ prototyping boards. This is a stripboard product that features horizontal traces on one side and vertical on the other, which lends itself to compactness.

On top of [Mark]’s computer are the processor and EPROM, while on the lower board are the RAM, UART, clock, and address decoding logic. It runs at 1.8 MHz, has 16 kB of ROM and 32 kB of RAM, which seems inconsequential in 2017 but would have been a rather impressive spec in the early 1980s.

There are three rows of pins connecting the boards, with the address bus carried up the middle and everything else at the edges. He’s toying with the idea of a third layer containing a keyboard and video display driver, something to look forward to.

The computer isn’t all on the page though, rather than wait for one to arrive he’s built his own EPROM programmer on a breadboard. He doesn’t have an eraser though, so has resorted to the Australian sunshine to (slowly) provide the UV light he needs.

We’ve featured other [Grant Searle] designs before, including a Sony Watchman clock with a Z80 board behind it, and another tiny board, this time with a Z80 rather than a 6502.

12 thoughts on “A 6502 Retrocomputer In A Very Tidy Package

    1. Flash technology didn’t exist back in the days of the 6502. IIRC, it was around 1982 that I was developing Intel 8051 products using the 8751 for prototypes. It’s an NMOS 8051 with EPROM instead of mask ROM, and a price tag over A$100 ea @ 40 off. (And that’s 1982 dollars!) It ran toasty warm. When CMOS 8051s came along, and they ran cool, it was a miracle. But you lost almost all the I/O if using the 8051 as an 8031, and adding an external EPROM.

      For production, the code was masked into ROM in the silicon foundry. Code errors were strictly inadmissible, as there was no way to change anything once it’s in the metalisation patterns.

      1. I know the history, but why, for new retrocomputing designs, not simply flash?
        That way you can even program them on the fly, new firmware into RAM, flasher into RAM, execute and voila, we have an update.

        1. It’s possible, but different people have different interpretations of the word retro. Some like to use only components that were available at the time. Others use modern chips, like an AVR or Propellor chip as the memory, or even an FPGA.

          1. “different people have different interpretations of the word retro”

            Exactly. That can vary from an emulation running on a dirt cheap Android tablet at many times the original, native speed, to an FPGA functional equivalent, to retro hardware using only period electronics as with this example. It’s like restoring an actual Shelby Cobra versus building a kit version on a modern chassis.

      2. I remember masked ROMs. One company I worked for in the early 90’s used Motorola 68HC05-series processors, including a ROM version. As I recall it cost about $7k to create a ROM version of the product. ROM versions were only used when production quantity and software maturity allowed for it (master copies of the software were kept on 5 1/4″ floppies stored in a vault with Mu-metal shielding.

        One interesting project I got to lead the upgrade from the 68HC705P3 to 68HC705C8. Not only was it half price, but it had additional I/O (28 pin to 40 pin) so I was able to eliminate a lot of glue logic. Most projects I did there involved evaluating alternative sources and components. Not all engineering jobs involving building girl robots to take to the prom!

        The development version was conventional EPROM, but the production version (with the cost savings) was just a plastic DIP. One production batch were all defective because something happened to the master that “we” were copying. Not much cost savings if you make a batch of defects.

  1. A bit off topic, but those Perf+ boards look great… I wish I had them last weekend when I spent a day soldering jumpers all ower the place!
    Does anybody know if they are available online somewhere? (preferably in Europe)
    I tried the original website but I get “not in stock” when trying to do the order.


    Back to the project of this post:
    looks neat, love this retro projects! (…and I have a 6502 bought from ebay a while ago waiting for me to do something with it!)

      1. Thank you for the reply, just placed an order for 20 boards.
        Shipping costs are pretty high though (~$30, argh), wouldn’t make sense to look for a reseller in Europe?

        Anyway, good product and worth the money!

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