PSION II Teardown – Retro Tech for those Yuppies of the 80’s

The PSION II was the worlds first PDA (Personal Digital Assistant) and was revolutionary in its time. In reality it was next to useless for most things but if you persisted you could store your contacts in it at a push. In this video I take it apart to have a look inside at that 80’s 8-bit computing excellence, break it and repair it along the way.

The architecture is basically a simple 8-bit computer based on a Hitachi HD6301 CPU (now obsolete of course) which was a CMOS version of the now legendary 6800 microprocessor. The CPU running at just under 1MHz along with a couple of EPROMS and some SRAM make up the entire system, very simplistic by todays standards. The portability was made possible because of both the CMOS technology as well as surface mount components which were are relatively new innovation at the time.

The system used Data Packs which at the time were quite expensive. A Data Pack is essentially an EPROM while a RAM pack is a battery backed SRAM chip. These packs are in small cartridges and the PSION II could have two cartridges loaded at any one time. When the Data Pack got full you had to remove the small board from the cartridge and expose the internal EPROM’s window to UV light – not sure how PSION got away with marketing this but I suppose at the time thats all that could be achieved for permanent storage in such a small package.

This is a very hackable device but when all said and done – what would you use it for. The one thing it could be converted to is a portable EPROM programmer, that would not take much effort but EPROMS are not really much use now days. So with nostalgia set aside I cannot think of any sensible use for this (except donating to a computing museum perhaps) so its going into the garage on the “Of no earthly use but too nice to throw away/scrap”!

I found some useful links on the web which describe the technical and user details of these machines which I have provided below.

This content is published under the Attribution-Noncommercial-Share Alike 3.0 Unported license.


File Description File size Downloads
pdf HD6301 8-bit MCU Microprocessor data sheet
2 MB 2593


  1. Nice tear down and repair as usual Gerry…BTW, finished up my Rb standard box; works fine but did decide to use a bi-color LED for the unlock/lock indicator instead of the micro for the first go ’round until I learn more about MPLAB. If you’re interested I’ll forward my project note for our local amateur radio club.


      1. Gerry – send along your e-mail so I can forward the note when I finish it up later today (I don’t see a contact option on the page). [or however you want to receive stuff from blog followers]

  2. Gerry,
    With voyger1 being in the news over the last few days i suppose it’s worth think that the guys who built that spacecraft could have used the the small cpu it would probably seemed like magic
    rather than the slide rules they would mostly have been using, though nowadays i suspect a lot of watches have more powerfull micro’s

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