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Commodore PET Projects - petSD+


Getting from this to this
Photo : Commodore Computer Online Museum    

Jump to petSD+ availability

Breaking News : 15/03/2016

Nils has now added IEC support to petSD+ - use it with your Commodore 64 etc. too !


Last Firmware Update : 01/12/2016 Get it here

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Commodore PETs initially used compact cassette tape for loading and saving programs and data, later machines used floppy disk systems such as the 8250 twin DS/QD 5.25" disk system that I obtained with my PET, shown in the photo above. The 8250 uses full height drives and a format unique to the PET - the drive cannot even read or write disks from other Commodore disk systems such as the 1541.

Nowadays, there are a number of floppy disk hardware emulators, such as the HxC Floppy Disk emulator, that can be used to replace "standard" floppy disk devices based on the Shugart interface. The non-standard nature of the PET floppy disk system means that there are a very limited number of options available for the PET, including petSD+ designed by Nils Eilers. (Some other options are described on my petSD+ Alternatives page.)

Quoting from Nils' webpage, "A petSD is a modern mass storage solution for Commodore PETs with an IEEE-488-bus. It can be used instead of and alongside vintage floppy disk drives. The petSD makes file sharing between the PET and the PC easy by using standard SD cards for storage."

Further technical details can be found on my petSD+ Hardware page.

Note: petSD+ was not designed to be used with devices equipped with a Commodore serial bus such as the Commodore 64, there are already a number of compatible devices available such as MMC2IEC, SD2IEC or uIEC and Nils had not envisaged anyone wanting to use petSD+ with serial bus devices. However, one use asked Nils if it were possible and Nils has included an IEC option in the firmware - see here for details.


petSD Availability - 2015 (as petSD+)

Although my initial interest was driven by my desire to get a petSD for myself, with Nils' permission, I am now in a position to make petSD+ available to anyone else who might be interested. (You can read about how I got into this and the current status of petSD+ on my petSD+ History page.)



petSD was designed to be constructible by the average electronics hobbyist, and one of the design goals was to be able to use through-hole-technology (THT) components, rather than surface mount chips. The one exception was the FT232RL USB-serial-adapter for which a THT equivalent was not available. The USB - serial adapter has been dropped from the petSD+ design, the only surface mount component remaining is the SD card reader.

Assembly of the petSD+ kit is described on the Assembly page.

 When I asked for input on the prospective supply options, based on the limited number of responses, supplying a kit of parts seemed to be the most popular choice. I decided that I would make kits available, as well as pre-assembled units for folks who need one. In practice though, once the kits and pre-assembled units became available, the majority of people wanted a pre-built one.

A modified version 2 PCB is currently being designed by Nils, but this may take a little while to make it into production. In the meantime, a slightly modified version "1a" board has been produced that corrects the MISO connection issue described in Nils' errata link on his web page. (This issue is only relevant to petSD+ boards that have the ISP port connector fitted which will not be needed by most users anyway).

Kits of parts and fully assembled petSD+ devices based on the Version 1.1 PCB are now available for purchase :


Please see the Ordering page for details





References :

Nils Eilers petSD home page

Donald's internet shop

The Vintage Computer Forums - petSD thread


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