Using 30 Year Old Microcontrollers


Like a lot of electronic tinkerers, [Andrew] has a lot of ancient components floating around his parts bin. His latest rediscovery in his cornucopia of components are a few Intel MCS-48 microcontrollers, dating back to 1977. Along with a few old EPROMs, [Andrew] decided it was worth getting these chips running again, if only for a historical curiosity.

[Andrew]’s had a few Intel 8035L microcontrollers on his hands, but this particular model of MCS-48 micros lacks any way to store code. This is where the EPROMs come in. With a modern EPROM programmer, [Andrew] was able to write some code to the extremely common for their vintage 27256 EPROMs. Erasing them, though, does require a UV lamp.

With the ROM programmed and the chips connected, [Andrew] was able to make a simple blinking LED circuit. Sure, it’s the simplest thing you can do with a microcontroller, but [Andrew]’s off to a great start in his explorations of older hardware.

28 thoughts on “Using 30 Year Old Microcontrollers

    1. In the early 80’s I used these chips for comercial development. Back in those days every byte of RAM and ROM were precious resources and you had to put a lot of thought into packing as much as you could into your programming.

      The biggest code I every did with an 8048 was a dual stepper motor driver with multitasking and profiled motion on both axis. Packing all that in was a real challenge. Also, if you look at the datasheet you will see the power consumption of the pre-CMOS chips was very high (100 mA?). They cost about $35 each back then. A $1 PIC would run rings around that old chip and only draw 2 mA.

      And we had a mechanical crank on the side of the chip to get it going on cold mornings =-}.

    1. I learned embedded programming in the late 1970’s. We used an 8085. We “hand assembled” the code by using a sheet of paper that had the assembly instructions and their corresponding hex code. We would write the program on a sheet of paper, translate it into binary (including calculating the jumps), and then load the program into a RAM in code space with switches. Then you flip a switch to run the code. It was painfully slow to write a program.

      It was wonderful when we graduated into using an assembler program.

  1. It is nice to have 64kB of SRAM and 32kB of EPROM, but 8048 has only 12-bit wide PC. Addresssing 64kB of SRAM is not trivial nor very usable. Yes, you can do bank switching, but it is somehow cumbersome.

    On the other hand, I have a lot of 70’s and 80’s MCUs and CPUs and I love this technology, though I’m younger than most of my collection.

  2. Please don’t make this a new fad! I have 4 AM2901DC bit slice processors from around 1980 or earlier. They are 4-bits wide and packaged in white ceramic with gold lids. Look pretty cool. I can build a 16-biter out of them.
    I have 3 TMP8243P (bus expanders, I think). Not sure if they only work with 8086 or what. If you can use them, I’ll send them.

  3. At college, I build a single “protoboard” microcomputer using an intel 8051 microcontroller. It was funny because I made a serial bootloader, to upload the compiled .hex from the serial port to RAM, and execute them. With this microcontrollers, you really know the deep working of actual micros.

  4. its finding a use for them thats the trick, One of the most popular firmwares I use on my avrs is for turning an avr into generic io via serial, I can set pins to input or output, read adc etc. It gets pretty hard when your limited to what the old micros have.

    1. You can add all those features to a 70’s/80’s vintage micro using additional 74 series logic and/or the peripheral chips sets for the micro family in question – it’s not hard, and 74 series chips are still widely available. If you wanted to get fancy you could use an FPGA, but that wouldn’t be authentic. Granted, a lot more work than a one or two chip solution we are used to these days, but it can be done.

  5. Hi … Ihave some parts from an old 1970s am fm cassete recorder vinyl record player with stereo and seen some chips in there and am wondering if you’d be able to help me identify them .. as in some raw support type of thing

  6. One of the very early Intel manuals had this classic when describing the allowable characters in the assembly language symbols names:

    “A well placed underscore can make the difference between a s_exchange and a sex_change.”

    Unlike the boring manuals of today the manuals of that era actually tried to teach.
    For example the 8048 Assembly Language Reference Manual uses a post office mailbox analogy to describe addressing modes and label usages:

  7. I still work on these processors for work. I write automatic tests for old machinery in a famous cigarette companies factory sometimes and there boards have ancient components. although i rarely write code for them (i usually use a cpu emulator in the boot rom) i have found it to be fun.

  8. HOLY FREAKING KITTENS BATMAN! Did HaD just acknowledge that microcontrollers existed before the ARDUINO!? let alone acknowledge that there ARE other microcontrollers!? Did Parallax ™ put up the 500k for this site!? come on now!

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